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2017 Volume 75 Issue 11
2017, 75(11): 1021-1022
doi: 10.6023/A1711E001
Abstract:
2017, 75(11): 1029-1035
doi: 10.6023/A17060259
Abstract:
Sensors are core components for modern intelligent industry. Thermoelectric materials, which have significant influence on the design and functions for a variety types of sensors, attracted more and more attentions recently. In this paper, different categories of thermoelectric materials, such as silicon, carbon, lead, tellurium, precious metal, organic and catalysis based thermoelectric materials, are discussed in detail on their high sensitivity, fast response, and stability as potential candidates for specific sensors. The silicon-based thermoelectric materials are of particular efficiency in sensor data process and transmission due to their high purity. Carbon-based thermoelectric materials, including graphene and carbon nanotubes, advantage in their excellent conductivity, flexible structure, and manufactural controllability. Lead-based thermoelectric materials are mainly used as infrared sensors because of their natural sensitivity to infrared specially. Telluride-based thermoelectric materials, especially Bismuth Telluride and Antimony Telluride, can form PN junction and be applied as soft sensors. Products based on these materials have already been developed for detecting pulses. The precious metals-based thermoelectric materials, e.g. gold or silver, are commonly used as dopant in the organic thermoelectric materials to adjust their sensitivity. Organic thermoelectric materials benefit from their good stability and variability, while copper-bismuth alloy based thermoelectric materials are widely investigated to make gas sensors. In general, the inorganic thermoelectric materials normally feature high electrical conductivity, which enhances the sensitivity of sensors, whereas the organic thermoelectric materials have high stability to maintain the stability of sensors. At present, the miniaturization of sensors is the mainstream for both material study and device fabrication. Low dimensional thermoelectric materials, especially nano-scaled materials such as quantum dots, nanowires, etc., will for sure promote the progressing of sensor development. For example, carbon nanotube can be knit into specific sheets as we designed with tunable conductivity, which makes them of remarkable industrial potentials as soft sensors. Designing and fabricating multi-functional and space-saving thermoelectric materials with well aligned and effectively assembled nanomaterials would be a feasible and practicable approach for future sensors.
Sensors are core components for modern intelligent industry. Thermoelectric materials, which have significant influence on the design and functions for a variety types of sensors, attracted more and more attentions recently. In this paper, different categories of thermoelectric materials, such as silicon, carbon, lead, tellurium, precious metal, organic and catalysis based thermoelectric materials, are discussed in detail on their high sensitivity, fast response, and stability as potential candidates for specific sensors. The silicon-based thermoelectric materials are of particular efficiency in sensor data process and transmission due to their high purity. Carbon-based thermoelectric materials, including graphene and carbon nanotubes, advantage in their excellent conductivity, flexible structure, and manufactural controllability. Lead-based thermoelectric materials are mainly used as infrared sensors because of their natural sensitivity to infrared specially. Telluride-based thermoelectric materials, especially Bismuth Telluride and Antimony Telluride, can form PN junction and be applied as soft sensors. Products based on these materials have already been developed for detecting pulses. The precious metals-based thermoelectric materials, e.g. gold or silver, are commonly used as dopant in the organic thermoelectric materials to adjust their sensitivity. Organic thermoelectric materials benefit from their good stability and variability, while copper-bismuth alloy based thermoelectric materials are widely investigated to make gas sensors. In general, the inorganic thermoelectric materials normally feature high electrical conductivity, which enhances the sensitivity of sensors, whereas the organic thermoelectric materials have high stability to maintain the stability of sensors. At present, the miniaturization of sensors is the mainstream for both material study and device fabrication. Low dimensional thermoelectric materials, especially nano-scaled materials such as quantum dots, nanowires, etc., will for sure promote the progressing of sensor development. For example, carbon nanotube can be knit into specific sheets as we designed with tunable conductivity, which makes them of remarkable industrial potentials as soft sensors. Designing and fabricating multi-functional and space-saving thermoelectric materials with well aligned and effectively assembled nanomaterials would be a feasible and practicable approach for future sensors.
2017, 75(11): 1036-1046
doi: 10.6023/A17060289
Abstract:
The localized surface plasmon resonance of metal nanoparticles is the collective oscillation of electrons on particle surface. The localized electromagnetic interaction brings a series of novel functions and applications. Plasmonic nanomaterials have been the significant part of nanophotonics, since its' localized surface plasmon resonance (LSPR) can focus incident phonons on the nanoscale surface. The unique plasmonic property is highly sensitive to their size, shape, coupling between particles as well as local dielectric environment. These properties can be utilized for the development of new biosensing and bioimaging applications. To date, many LSPR sensing strategies have been developed with outstanding measurement capabilities, enabling detection down to the single-molecule level, including LSPR-based sensing, surface-enhanced Raman scattering, metal-enhanced fluorescence, dark-field light-scattering, metal-mediated fluorescence resonance energy transfer. Moreover, the unique optical stability of plasmonic nanoparticles enables them as ideal probes in cellular imaging. Here, recent examples on application of plasmonic nanostructures in sensing and bioimaging are summarized, and perspectives are provided as well.
The localized surface plasmon resonance of metal nanoparticles is the collective oscillation of electrons on particle surface. The localized electromagnetic interaction brings a series of novel functions and applications. Plasmonic nanomaterials have been the significant part of nanophotonics, since its' localized surface plasmon resonance (LSPR) can focus incident phonons on the nanoscale surface. The unique plasmonic property is highly sensitive to their size, shape, coupling between particles as well as local dielectric environment. These properties can be utilized for the development of new biosensing and bioimaging applications. To date, many LSPR sensing strategies have been developed with outstanding measurement capabilities, enabling detection down to the single-molecule level, including LSPR-based sensing, surface-enhanced Raman scattering, metal-enhanced fluorescence, dark-field light-scattering, metal-mediated fluorescence resonance energy transfer. Moreover, the unique optical stability of plasmonic nanoparticles enables them as ideal probes in cellular imaging. Here, recent examples on application of plasmonic nanostructures in sensing and bioimaging are summarized, and perspectives are provided as well.
2017, 75(11): 1047-1060
doi: 10.6023/A17080353
Abstract:
Nucleic acids, including deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), play important roles in normal or abnormal life activities. DNA is an important genetic material and carrier of genetic information. It plays an important role in cell division, biological development, mutation, cancer, etc. RNA includes mRNA, tRNA, microRNA (miRNA) and small RNA. Tumor-associated mRNA has been widely used as a specific marker to assess the migration of tumor cells, and its expression level is related to the tumor burden and malignant progression. MiRNA is a non-coding small molecule RNA that regulates at least 30% of the genes. MiRNA is involved in most of the biological process, such as proliferation, differentiation, senescence, migration and apoptosis. The abnormal expression of DNA, mRNA and miRNA is closely associated with the occurrence and development of multiple diseases. Therefore, developing accurate and effective methods for detecting nucleic acid molecules is of great significance for studying the function of nucleic acid regulation and achieving the early detection and treatment of diseases. Fluorescence detection method and imaging technology provide powerful tools for real-time and accurately detecting nucleic acid molecules due to their high sensitivity and temporal resolution. Fluorescent nanoprobe has many advantages such as good biocompatibility, good solubility and so on. It has been widely used in the detection of nucleic acid molecules for further understanding the roles of nucleic acid in many diseases. In this review, we have showed the roles of various nucleic acid molecules in life activities and illustrated the advances in the development of fluorescent nanoprobe for detection of disease-related DNA, mRNA and miRNA in live cells and in vivo in recent years. The preparation of these nanoprobe, detection mechanism and imaging application were also presented. Finally, the challenge and future development of constructing new fluorescent nanoprobe for nucleic acids detection were proposed.
Nucleic acids, including deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), play important roles in normal or abnormal life activities. DNA is an important genetic material and carrier of genetic information. It plays an important role in cell division, biological development, mutation, cancer, etc. RNA includes mRNA, tRNA, microRNA (miRNA) and small RNA. Tumor-associated mRNA has been widely used as a specific marker to assess the migration of tumor cells, and its expression level is related to the tumor burden and malignant progression. MiRNA is a non-coding small molecule RNA that regulates at least 30% of the genes. MiRNA is involved in most of the biological process, such as proliferation, differentiation, senescence, migration and apoptosis. The abnormal expression of DNA, mRNA and miRNA is closely associated with the occurrence and development of multiple diseases. Therefore, developing accurate and effective methods for detecting nucleic acid molecules is of great significance for studying the function of nucleic acid regulation and achieving the early detection and treatment of diseases. Fluorescence detection method and imaging technology provide powerful tools for real-time and accurately detecting nucleic acid molecules due to their high sensitivity and temporal resolution. Fluorescent nanoprobe has many advantages such as good biocompatibility, good solubility and so on. It has been widely used in the detection of nucleic acid molecules for further understanding the roles of nucleic acid in many diseases. In this review, we have showed the roles of various nucleic acid molecules in life activities and illustrated the advances in the development of fluorescent nanoprobe for detection of disease-related DNA, mRNA and miRNA in live cells and in vivo in recent years. The preparation of these nanoprobe, detection mechanism and imaging application were also presented. Finally, the challenge and future development of constructing new fluorescent nanoprobe for nucleic acids detection were proposed.
2017, 75(11): 1061-1070
doi: 10.6023/A17070342
Abstract:
Single nanoparticle sensing (SNS) is an emerging research field which utilizes single nanoparticles as individual nano-sensors to acquire the qualitative and quantitative information of the analytes in a localized and microscopic sample environment. Both the molecular recognition and signal transduction take place at the surface of a single nanoparticle. Versatile kinds of optical microscopy, such as dark-field microscopy and fluorescence microscopy, are often applied to locating the nano-sensor, and to accessing and analyzing the optical signal it reports. Compared to traditional sensing mechanisms that rely on ensemble nanomaterials, SNS has demonstrated its excellent sensitivity down to single molecule detection by focusing in extremely small volumes in the range of aL~pL. Simultaneous monitoring on many individual nano-sensors in a nano-array further allows for high-throughput and multiplex analysis. More importantly, single nanoparticles can be easily introduced to microscopic and dynamic systems such as living cells to probe specific analytes with high temporal and spatial resolution while maintaining the excellent sensitivity. In this review, we begin with a brief introduction on the history and development of SNS, which is followed by its major features. We subsequently survey the recent progresses in this field in the past five years, focusing on the different sensing principles, single nanoparticle counting and single nanoparticle tracking. We finally provide our perspectives that further developments on nano-probes, optical imaging techniques and data analysis are critical to the growth and applications of SNS in broad fields.
Single nanoparticle sensing (SNS) is an emerging research field which utilizes single nanoparticles as individual nano-sensors to acquire the qualitative and quantitative information of the analytes in a localized and microscopic sample environment. Both the molecular recognition and signal transduction take place at the surface of a single nanoparticle. Versatile kinds of optical microscopy, such as dark-field microscopy and fluorescence microscopy, are often applied to locating the nano-sensor, and to accessing and analyzing the optical signal it reports. Compared to traditional sensing mechanisms that rely on ensemble nanomaterials, SNS has demonstrated its excellent sensitivity down to single molecule detection by focusing in extremely small volumes in the range of aL~pL. Simultaneous monitoring on many individual nano-sensors in a nano-array further allows for high-throughput and multiplex analysis. More importantly, single nanoparticles can be easily introduced to microscopic and dynamic systems such as living cells to probe specific analytes with high temporal and spatial resolution while maintaining the excellent sensitivity. In this review, we begin with a brief introduction on the history and development of SNS, which is followed by its major features. We subsequently survey the recent progresses in this field in the past five years, focusing on the different sensing principles, single nanoparticle counting and single nanoparticle tracking. We finally provide our perspectives that further developments on nano-probes, optical imaging techniques and data analysis are critical to the growth and applications of SNS in broad fields.
2017, 75(11): 1071-1081
doi: 10.6023/A17070300
Abstract:
Optical sensors are devices that transform the interaction between medium and analyte to optical signal. Optical interference is a technique that has been widely applied in optical sensors, which is label-free, fast and non-invasive. Light reflected from the top and bottom surfaces of single layer film, or each interfaces of multilayer film in optical sensors leads to constructive and destructive fringes of the optical interference pattern. Nanoporous films with large surface-to-volume ratio are beneficial to improve the sensitivity and lower the limit of detection of the sensors, which is typically used in the form of single layer, double layer or multilayer (usually served as photonic crystal). In this article, we introduce and review the applications of nanoporous films of silicon, anodic aluminum oxide, titanium dioxide and metal-organic framework in optical sensors based on the optical interference. A perspective of developments in this research field is also provided.
Optical sensors are devices that transform the interaction between medium and analyte to optical signal. Optical interference is a technique that has been widely applied in optical sensors, which is label-free, fast and non-invasive. Light reflected from the top and bottom surfaces of single layer film, or each interfaces of multilayer film in optical sensors leads to constructive and destructive fringes of the optical interference pattern. Nanoporous films with large surface-to-volume ratio are beneficial to improve the sensitivity and lower the limit of detection of the sensors, which is typically used in the form of single layer, double layer or multilayer (usually served as photonic crystal). In this article, we introduce and review the applications of nanoporous films of silicon, anodic aluminum oxide, titanium dioxide and metal-organic framework in optical sensors based on the optical interference. A perspective of developments in this research field is also provided.
2017, 75(11): 1082-1086
doi: 10.6023/A17090402
Abstract:
Steady-state cyclic voltammetry has several advantages that make it extremely useful for characterization of ultramicroelectrodes, such as rapid electrode performance assessment and size determination. However, due to the nanoscale size effect, the slight variations in geometry of the nanoelectrodes can lead to significant perturbations in its performance. In this study, electrochemical experiments and finite-element simulations using COMSOL Multiphysics software were conducted to characterize the steady-state current dependence on electrode radii, geometries and recesses. To study the above characterics, the Pt nanodisk electrodes with different sizes were fabricated using a laser-assisted wire pulling method on a P-2000 laser puller. Sluggish current responses were obtained for electrodes with a radius smaller than 80 nm in a 5 mmol/L ferrocene (Fc) CH3CN electrolyte solution containing 0.2 mol/L Tetra-n-butylammonium hexafluorophosphate (TBAPF6). The experimental results agree very well with the simulations. It was discovered that the sluggish responses are due to the kinetically limited electron transfer resulting from the slow reaction rate relative to diffusion. Moreover, a minimum, constant steady state current value was measured once the RG value (i.e., the ratio of overall electrode radius to active electrode radius) was greater than 3. However, the current increased obviously with the RG value decreased below this value due to the enhanced mass transport. In addition, the steady-state voltammetric responses of recessed nanoelectrodes were investigated. It was found that the steady-state current decreased rapidly as the recess depth increased and a classical sigmoidal shape current response was obtained recovering from a sluggish current response. The unique current responses resulted from the restriction of the diffusion of redox molecules in a deep channel to the electrode. To verify the correlation of recess depth to current response, a model was built based on two-dimensional axial symmetry and the obtained simulation results were consistent well with the experimental data. Our findings offer an understanding on the relationship between the nanoelectrode geometry and steady-state cyclic voltammetry, which can provide insight into their electrochemical behaviors.
Steady-state cyclic voltammetry has several advantages that make it extremely useful for characterization of ultramicroelectrodes, such as rapid electrode performance assessment and size determination. However, due to the nanoscale size effect, the slight variations in geometry of the nanoelectrodes can lead to significant perturbations in its performance. In this study, electrochemical experiments and finite-element simulations using COMSOL Multiphysics software were conducted to characterize the steady-state current dependence on electrode radii, geometries and recesses. To study the above characterics, the Pt nanodisk electrodes with different sizes were fabricated using a laser-assisted wire pulling method on a P-2000 laser puller. Sluggish current responses were obtained for electrodes with a radius smaller than 80 nm in a 5 mmol/L ferrocene (Fc) CH3CN electrolyte solution containing 0.2 mol/L Tetra-n-butylammonium hexafluorophosphate (TBAPF6). The experimental results agree very well with the simulations. It was discovered that the sluggish responses are due to the kinetically limited electron transfer resulting from the slow reaction rate relative to diffusion. Moreover, a minimum, constant steady state current value was measured once the RG value (i.e., the ratio of overall electrode radius to active electrode radius) was greater than 3. However, the current increased obviously with the RG value decreased below this value due to the enhanced mass transport. In addition, the steady-state voltammetric responses of recessed nanoelectrodes were investigated. It was found that the steady-state current decreased rapidly as the recess depth increased and a classical sigmoidal shape current response was obtained recovering from a sluggish current response. The unique current responses resulted from the restriction of the diffusion of redox molecules in a deep channel to the electrode. To verify the correlation of recess depth to current response, a model was built based on two-dimensional axial symmetry and the obtained simulation results were consistent well with the experimental data. Our findings offer an understanding on the relationship between the nanoelectrode geometry and steady-state cyclic voltammetry, which can provide insight into their electrochemical behaviors.
2017, 75(11): 1087-1090
doi: 10.6023/A17090433
Abstract:
MicroRNAs (miRNAs), 18~22 nucleotides in length, are a class of single-strand noncoding short RNAs and have been used as biomarkers for diagnosis and prognosis of cancers. Herein, an α-hemolysin (α-HL) nanopore was adapted for the colorectal cancer-associated miRNAs analysis, with the merits of high-throughput, ultra-sensitivity and no requirements of amplification/labelling. DNA probes, consisting of a signal tag in each end and a response element in the middle section, were designed. The response element could be well-matched with miRNA and utilized for specific recognition of the target miRNA, while the signal tag increased the capture rate of the miRNA·probe complex. Due to the poor stacking of thymine residues, poly(dT)n need to overcome a high entropic barrier when traversing through the α-HL nanopore confined space, resulting in distinct double-level blocked events, which contributes to the visualized differences in signal shape and prolonged duration. Thus, poly(dT)n was selected as the signal tag of probe. Added in the cis side of α-HL, miRNA·probe was forced to traverse across the nanopore confined space under the potential of 140 mV through a pair of Ag/AgCl electrodes (cis grounded). Typical three-stage blocked event was observed, reflecting the translocation process:capture and dissociation of miRNA·probe, translocation of probe, temporarily residence and translocation of miRNA. Stage 1 (S1) represented the process from capture of miRNA·probe complex to translocation of the entire probe. The typical blocked events of miRNA 92·probe 92 showed a two-level S1, where Level 1 (L1) with a current blockage of 0.57±0.01 was generated mainly by translocation of the poly(dT)40 signal tag. As the duration is associated with DNA length, probe 21 with smaller poly(dT)20 signal tag was designed to detect miRNA 21, resulting in a shorter L1 of miRNA 21·probe 21 whose duration (tD-L1) was 1/3 of that for miRNA 92·probe 92. As the signal shapes vary with DNA sequences, probe 16 with signal tag of poly(dC)40 was used to sense miRNA 16, with miRNA 16·probe 16 producing a different single-level S1 with miRNA 92·probe 92 and miRNA 21·probe 21. The statistical results demonstrated that the three kinds of miRNA·probe produced different durations for S1 (tD-S1), possibly indicating the differences in probe-α-HL interaction. Therefore, miRNA 92, miRNA 21 and miRNA 16 could be well identified by tD-L1 (signal shape) and tD-S1 (duration). Moreover, the serum sample have been tested. Hence, α-HL nanopore can be applied to build ultrasensitive single molecule biosensor for miRNA.
MicroRNAs (miRNAs), 18~22 nucleotides in length, are a class of single-strand noncoding short RNAs and have been used as biomarkers for diagnosis and prognosis of cancers. Herein, an α-hemolysin (α-HL) nanopore was adapted for the colorectal cancer-associated miRNAs analysis, with the merits of high-throughput, ultra-sensitivity and no requirements of amplification/labelling. DNA probes, consisting of a signal tag in each end and a response element in the middle section, were designed. The response element could be well-matched with miRNA and utilized for specific recognition of the target miRNA, while the signal tag increased the capture rate of the miRNA·probe complex. Due to the poor stacking of thymine residues, poly(dT)n need to overcome a high entropic barrier when traversing through the α-HL nanopore confined space, resulting in distinct double-level blocked events, which contributes to the visualized differences in signal shape and prolonged duration. Thus, poly(dT)n was selected as the signal tag of probe. Added in the cis side of α-HL, miRNA·probe was forced to traverse across the nanopore confined space under the potential of 140 mV through a pair of Ag/AgCl electrodes (cis grounded). Typical three-stage blocked event was observed, reflecting the translocation process:capture and dissociation of miRNA·probe, translocation of probe, temporarily residence and translocation of miRNA. Stage 1 (S1) represented the process from capture of miRNA·probe complex to translocation of the entire probe. The typical blocked events of miRNA 92·probe 92 showed a two-level S1, where Level 1 (L1) with a current blockage of 0.57±0.01 was generated mainly by translocation of the poly(dT)40 signal tag. As the duration is associated with DNA length, probe 21 with smaller poly(dT)20 signal tag was designed to detect miRNA 21, resulting in a shorter L1 of miRNA 21·probe 21 whose duration (tD-L1) was 1/3 of that for miRNA 92·probe 92. As the signal shapes vary with DNA sequences, probe 16 with signal tag of poly(dC)40 was used to sense miRNA 16, with miRNA 16·probe 16 producing a different single-level S1 with miRNA 92·probe 92 and miRNA 21·probe 21. The statistical results demonstrated that the three kinds of miRNA·probe produced different durations for S1 (tD-S1), possibly indicating the differences in probe-α-HL interaction. Therefore, miRNA 92, miRNA 21 and miRNA 16 could be well identified by tD-L1 (signal shape) and tD-S1 (duration). Moreover, the serum sample have been tested. Hence, α-HL nanopore can be applied to build ultrasensitive single molecule biosensor for miRNA.
2017, 75(11): 1091-1096
doi: 10.6023/A17070330
Abstract:
Electrode fouling and passivation is an inevitable problem which seriously affects the electrode performance in cell culture and detection. Construction of photocatalytically renewable electrode by combination of nanophotocatalysts with electrochemical sensing materials could provide a promising approach for highly efficient renewal of electrode surface without damaging its micro-or nanostructures. However, the reactive oxygen species generated during photocatalysis always cause damages to cells being adhered or cultured on the electrode surface, which precludes on-line renewal of electrode during cell culture and detection. To address this issue, based on the visible light-induced renewable electrode (poly(3, 4-ethylenedioxythiophene) (PEDOT)-modified TiO2/CdS nanocomposites electrode we previously developed, a thin layer of gelatin hydrogel was spin-coated on the electrode in this work to realize efficient electrode renewal under visible light irradiation during the culture and detection of living cells. The optimized thickness (ca. 2 μm) of gelatin hydrogel was obtained by spin-coating under 3000 r/min. Benefitting from the network structure of gelatin hydrogel and the renewable performance of PEDOT@CdS/TiO2 nanocomposites, the gelatin coating efficiently blocked the diffusion of biomacromolecules from the bulk medium to the electrode surface and thus significantly diminished the fouling caused by these macromolecules, while the pollutants derived from small molecules could be efficiently degraded under visible light irradiation. Meanwhile, gelatin coating did not induce obviously decline in detection sensitivity, and a low detection limit of 4.2 nmol/L (S/N=3) could be obtained towards electrochemical detection of nitric oxide (NO). Most importantly, the gelatin layer efficiently blocked the ultrashort-lived but highly reactive oxygen species such as OH·(generated by photocatalytic process) diffusing from the electrode surface to the cells, and the damages to the cells caused by these highly reactive species could be therefore significantly decreased. The results from live/dead cell staining demonstrated that almost all the cells (>95%) cultured on gelatin-coated electrodes maintain their viability when the electrode was irradiated by visible light for 6 h, while a considerable part of cells (>40%) culture on the uncoated electrode lost their viability under the same conditions. These features allowed on-line renewal of the electrode during cell culture and detection as well as real-time monitoring of NO released from the human umbilical vein endothelial cells (HUVECs).
Electrode fouling and passivation is an inevitable problem which seriously affects the electrode performance in cell culture and detection. Construction of photocatalytically renewable electrode by combination of nanophotocatalysts with electrochemical sensing materials could provide a promising approach for highly efficient renewal of electrode surface without damaging its micro-or nanostructures. However, the reactive oxygen species generated during photocatalysis always cause damages to cells being adhered or cultured on the electrode surface, which precludes on-line renewal of electrode during cell culture and detection. To address this issue, based on the visible light-induced renewable electrode (poly(3, 4-ethylenedioxythiophene) (PEDOT)-modified TiO2/CdS nanocomposites electrode we previously developed, a thin layer of gelatin hydrogel was spin-coated on the electrode in this work to realize efficient electrode renewal under visible light irradiation during the culture and detection of living cells. The optimized thickness (ca. 2 μm) of gelatin hydrogel was obtained by spin-coating under 3000 r/min. Benefitting from the network structure of gelatin hydrogel and the renewable performance of PEDOT@CdS/TiO2 nanocomposites, the gelatin coating efficiently blocked the diffusion of biomacromolecules from the bulk medium to the electrode surface and thus significantly diminished the fouling caused by these macromolecules, while the pollutants derived from small molecules could be efficiently degraded under visible light irradiation. Meanwhile, gelatin coating did not induce obviously decline in detection sensitivity, and a low detection limit of 4.2 nmol/L (S/N=3) could be obtained towards electrochemical detection of nitric oxide (NO). Most importantly, the gelatin layer efficiently blocked the ultrashort-lived but highly reactive oxygen species such as OH·(generated by photocatalytic process) diffusing from the electrode surface to the cells, and the damages to the cells caused by these highly reactive species could be therefore significantly decreased. The results from live/dead cell staining demonstrated that almost all the cells (>95%) cultured on gelatin-coated electrodes maintain their viability when the electrode was irradiated by visible light for 6 h, while a considerable part of cells (>40%) culture on the uncoated electrode lost their viability under the same conditions. These features allowed on-line renewal of the electrode during cell culture and detection as well as real-time monitoring of NO released from the human umbilical vein endothelial cells (HUVECs).
2017, 75(11): 1097-1102
doi: 10.6023/A17060290
Abstract:
Mercury is very harmful to the environment and human health even at low concentration. Methods for sensitive detection of mercury ion (Hg2+) have increasingly been developed over the past decade owing to the rapid development in nanotechnology. However, the limits of detection (LODs) of these methods are mostly not satisfactory enough to meet the demand of monitoring trace amounts of mercury ion. DNA thymine (T bases) can react with the mercury ion to form T-Hg2+-T structure, and this interaction has been proved to be much more stable than the interaction between thymine and its complementary adenine (A bases). Based on this principle, a series of ultra-sensitive DNA-based colorimetric biosensors, mostly using Au nanoparticles (AuNPs) as DNA carriers, have been designed for detection of mercury ion. In this study, we report a new strategy for highly sensitive Hg2+ detection based on Hg2+-induced AuNPs assembly. AuNPs of different sizes (s-AuNPs of 18 nm and c-AuNPs of 52 nm) were modified with oligonucleotides containing a sequence of continuous T bases. In the presence of Hg2+, s-AuNPs would be bound to c-AuNPs in the solution owing to oligonucleotide hybridization, forming a core-satellites nanostrucure. This process was accompanied by a color change of the scattering light from green to orange as observed under dark-field microscopy and a corresponding distinct scattering peak shift. The scattering spectra of the AuNPs were obtained using a spectroscopic system which was established autonomously. The scattering peak shift of color-changed spots corresponded with Hg2+ concentration. It was increased linearly with logarithm of Hg2+ concentration over a wide range from 1 pmol/L to 1 nmol/L, with the correlation coefficient of 0.983 (R2=0.983), and the detection limit of Hg2+ was estimated to be 1 pmol/L. Other metal ions, such as Ag+, K+, Ca2+, Mg2+, Zn2+, Cd2+, Fe2+, Pb2+, Ni2+, Mn2+, Al3+, induced negligible scattering peak shifts for AuNPs under the same conditions, which showed that this strategy exhibited excellent selectivity towards Hg2+. Moreover, satisfactory results were obtained when the proposed approach was applied to detect Hg2+ in real samples with recoveries of 98.7%~103.1% and 105.6%~108.2% for river water and tap water, respectively.
Mercury is very harmful to the environment and human health even at low concentration. Methods for sensitive detection of mercury ion (Hg2+) have increasingly been developed over the past decade owing to the rapid development in nanotechnology. However, the limits of detection (LODs) of these methods are mostly not satisfactory enough to meet the demand of monitoring trace amounts of mercury ion. DNA thymine (T bases) can react with the mercury ion to form T-Hg2+-T structure, and this interaction has been proved to be much more stable than the interaction between thymine and its complementary adenine (A bases). Based on this principle, a series of ultra-sensitive DNA-based colorimetric biosensors, mostly using Au nanoparticles (AuNPs) as DNA carriers, have been designed for detection of mercury ion. In this study, we report a new strategy for highly sensitive Hg2+ detection based on Hg2+-induced AuNPs assembly. AuNPs of different sizes (s-AuNPs of 18 nm and c-AuNPs of 52 nm) were modified with oligonucleotides containing a sequence of continuous T bases. In the presence of Hg2+, s-AuNPs would be bound to c-AuNPs in the solution owing to oligonucleotide hybridization, forming a core-satellites nanostrucure. This process was accompanied by a color change of the scattering light from green to orange as observed under dark-field microscopy and a corresponding distinct scattering peak shift. The scattering spectra of the AuNPs were obtained using a spectroscopic system which was established autonomously. The scattering peak shift of color-changed spots corresponded with Hg2+ concentration. It was increased linearly with logarithm of Hg2+ concentration over a wide range from 1 pmol/L to 1 nmol/L, with the correlation coefficient of 0.983 (R2=0.983), and the detection limit of Hg2+ was estimated to be 1 pmol/L. Other metal ions, such as Ag+, K+, Ca2+, Mg2+, Zn2+, Cd2+, Fe2+, Pb2+, Ni2+, Mn2+, Al3+, induced negligible scattering peak shifts for AuNPs under the same conditions, which showed that this strategy exhibited excellent selectivity towards Hg2+. Moreover, satisfactory results were obtained when the proposed approach was applied to detect Hg2+ in real samples with recoveries of 98.7%~103.1% and 105.6%~108.2% for river water and tap water, respectively.
2017, 75(11): 1103-1108
doi: 10.6023/A17090407
Abstract:
Fluorescent DNA-stabilized Ag nanoclusters (DNA-Ag NCs), a class of excellent luminescence probes with excellent optical properties, have been applied in assorted sensing and imaging fields. To date, most of the quantifications were based on the direct signal change of DNA-Ag NCs caused by target recognition, which inevitably jeopardizes the reproducibility and robustness of methods when experimental settings or detecting conditions are changed. In this work, using the highly fluorescent G-quadruplex-stabilized Ag NCs (GQ-Ag NCs) and Cy5 as the donor-acceptor pair, we for the first time developed a FRET based ratiometric method for miRNA detection. A rationally optimized hairpin recognition structure was attached to the G-quadruplex template of the Ag nanocluster. The introduction of target sequence opened the hairpin, led to the approximation of the donor nanocluster and the acceptor Cy5, enabled the energy transfer between the FRET pair, and thus generated the optical signal change. The Cy5 tag sequence was designed to be universal, simplifying the experimental design and reduced the cost in applications. The optical signal for quantitation was determined by the signal difference between the Ag nanocluster and the Cy5 fluorophore, with the fluorescence intensity of Cy5 used as internal reference in order to prevent signal variation. MicroRNAs (miRNA) are short RNA molecules that have emerged as a kind of key post-translational regulators of gene expression in eukaryotic organisms. In this study, microRNA let-7a was chosen as the model target of our FRET-based ratiometric detection for demonstration. The linear range and the detection limit of the method on let-7a was 12~300 nmol/L and 6.9 nmol/L, respectively. The proposed method presented reasonable selectivity amongst the members of the same let-7 family. The remarkable recovery in total RNA extracted from HepG2 cell lines demonstrated the potential in clinical applications. The highlights of our work extended the application of DNA-templated Ag NCs and facilitated more understanding of DNA-Ag NCs as the energy donor in FRET design.
Fluorescent DNA-stabilized Ag nanoclusters (DNA-Ag NCs), a class of excellent luminescence probes with excellent optical properties, have been applied in assorted sensing and imaging fields. To date, most of the quantifications were based on the direct signal change of DNA-Ag NCs caused by target recognition, which inevitably jeopardizes the reproducibility and robustness of methods when experimental settings or detecting conditions are changed. In this work, using the highly fluorescent G-quadruplex-stabilized Ag NCs (GQ-Ag NCs) and Cy5 as the donor-acceptor pair, we for the first time developed a FRET based ratiometric method for miRNA detection. A rationally optimized hairpin recognition structure was attached to the G-quadruplex template of the Ag nanocluster. The introduction of target sequence opened the hairpin, led to the approximation of the donor nanocluster and the acceptor Cy5, enabled the energy transfer between the FRET pair, and thus generated the optical signal change. The Cy5 tag sequence was designed to be universal, simplifying the experimental design and reduced the cost in applications. The optical signal for quantitation was determined by the signal difference between the Ag nanocluster and the Cy5 fluorophore, with the fluorescence intensity of Cy5 used as internal reference in order to prevent signal variation. MicroRNAs (miRNA) are short RNA molecules that have emerged as a kind of key post-translational regulators of gene expression in eukaryotic organisms. In this study, microRNA let-7a was chosen as the model target of our FRET-based ratiometric detection for demonstration. The linear range and the detection limit of the method on let-7a was 12~300 nmol/L and 6.9 nmol/L, respectively. The proposed method presented reasonable selectivity amongst the members of the same let-7 family. The remarkable recovery in total RNA extracted from HepG2 cell lines demonstrated the potential in clinical applications. The highlights of our work extended the application of DNA-templated Ag NCs and facilitated more understanding of DNA-Ag NCs as the energy donor in FRET design.
2017, 75(11): 1109-1114
doi: 10.6023/A17070321
Abstract:
Acetylcholinesterase (AChE), as a key enzyme, ubiquitously exists in the peripheral nervous system. It mainly functions terminating neurotransmission at the cholinergic synapse through the rapid hydrolysis of acetylcholine (a neurotransmitter) into choline and acetate, which is intimately related to Alzheimer's disease, inflammatory processes, and nerve-agent poisoning. In this study, we developed a novel electrochemical method for probing AChE activity and screening its potential inhibitor based on the in-situ formation of thiocholine-Cu(Ⅱ) coordination polymer[denoted as TCh-Cu(Ⅱ) CP]. The detection mechanism is on the basis of the concept, that is, AChE could catalyze the hydrolysis of its substrate acetylthiocholine (ATCh) to produce a thiol-compound thiocholine (TCh). Subsequently, TCh reacted with Cu(Ⅱ) to form a positively charged TCh-Cu(Ⅱ) CP via S-Cu bond. Since the graphene (GO) is a negative compound due to its plenty of carboxyl groups, TCh-Cu(Ⅱ) CP could be adsorbed onto the graphene-modified glassy carbon electrode (GO/GCE) via electrostatic interaction. What's more, the CP/GO/GCE can electro-catalyze the O-phenylenediamine (OPD), generating a high current signal. We also conducted a series of experiments to verify the formation and electro-catalysis of TCh-Cu(Ⅱ) CP and investigated the selectivity of the TCh-Cu(Ⅱ) CP-based assay for AChE. As a result, it is clearly observed that the electrochemical response gradually increases with the increasing concentrations of AChE (0.05~100 mU·mL-1) and a detection limit of our method is estimated to be ca. 0.03 mU·mL-1 (S/N=3). Furthermore, compared to the traditional methods, our electrochemical assay has more simple detection procedure with better sensitivity and selectivity and has great potential in applications in many important areas, such as neurobiology, toxicology, and pharmacology, especially for the effective treatment of Alzheimer's disease.
Acetylcholinesterase (AChE), as a key enzyme, ubiquitously exists in the peripheral nervous system. It mainly functions terminating neurotransmission at the cholinergic synapse through the rapid hydrolysis of acetylcholine (a neurotransmitter) into choline and acetate, which is intimately related to Alzheimer's disease, inflammatory processes, and nerve-agent poisoning. In this study, we developed a novel electrochemical method for probing AChE activity and screening its potential inhibitor based on the in-situ formation of thiocholine-Cu(Ⅱ) coordination polymer[denoted as TCh-Cu(Ⅱ) CP]. The detection mechanism is on the basis of the concept, that is, AChE could catalyze the hydrolysis of its substrate acetylthiocholine (ATCh) to produce a thiol-compound thiocholine (TCh). Subsequently, TCh reacted with Cu(Ⅱ) to form a positively charged TCh-Cu(Ⅱ) CP via S-Cu bond. Since the graphene (GO) is a negative compound due to its plenty of carboxyl groups, TCh-Cu(Ⅱ) CP could be adsorbed onto the graphene-modified glassy carbon electrode (GO/GCE) via electrostatic interaction. What's more, the CP/GO/GCE can electro-catalyze the O-phenylenediamine (OPD), generating a high current signal. We also conducted a series of experiments to verify the formation and electro-catalysis of TCh-Cu(Ⅱ) CP and investigated the selectivity of the TCh-Cu(Ⅱ) CP-based assay for AChE. As a result, it is clearly observed that the electrochemical response gradually increases with the increasing concentrations of AChE (0.05~100 mU·mL-1) and a detection limit of our method is estimated to be ca. 0.03 mU·mL-1 (S/N=3). Furthermore, compared to the traditional methods, our electrochemical assay has more simple detection procedure with better sensitivity and selectivity and has great potential in applications in many important areas, such as neurobiology, toxicology, and pharmacology, especially for the effective treatment of Alzheimer's disease.
2017, 75(11): 1115-1120
doi: 10.6023/A17070337
Abstract:
Cell alignment plays a crucial role in the repair and regeneration of tissues, which is caused by the "contact guidance" of micro/nano structures. In this paper, the nano-grooves with 200 nm in width, 400 nm in period and 75 nm in depth were fabricated on gold substrate with the technique of nanoimprint to simulate the extracellular matrix (ECM). Electric cell-substrate impedance sensing (ECIS) was employed firstly to real-time monitor cell alignment of human foreskin fibroblasts (HFF) and human immortal keratinocyte cells (HaCaT) on nano-grooves, which are two important functional cell types in skin wound-healing. The cell images displayed that the nano-grooves could induce the alignment of HFF cells, in which, the cell arrangement along the direction of nano-grooves occurred prior to the cell elongation. While the nano-grooves couldn't influence the morphology of HaCaT cells, and their adhesion and spread were delayed. In the ECIS monitoring, HFF and HaCaT cells both presented increased normalized impedance (NI) values at their respective characteristic frequencies of 977 and 1465 Hz on nano-grooves and flat electrodes with the prolongation of culture time during 24 h and the increasing trends of NI values were also similar:in the first 6 h, NI values increased faster, and then, the increasing rates declined obviously. HFF cells on nano-grooves generated more intense impedance signals with a larger distinction of increasing rate than those on flat electrodes, indicating that the nano-grooves could promote the adhesion and spread of HFF cells and the directional arrangement had a larger impact on the variation of NI values than cell elongation. While HFF cells adhered and spread in random directions, leading to the reduced difference in increasing rate of NI values. The NI values of HFF cells was further correlated with cell alignment, showing the enhanced impedance responses with the rising percentage of aligned cells. More importantly, there was a good linear correlation between NI values and the percentage of cells arranging along the direction of nano-grooves. In contrast, HaCaT cells had smaller NI values on the nano-grooves with the similar increasing rates, compared to the flat electrodes, revealing that the nano-grooves were less suitable for the adhesion and spread of HaCaT cells with almost no change of cell morphology, and the cell adhesion could cause more obvious variation of NI values than cell spread. Our research would provide a support for the development of complex cell sensors based on ECIS and its application in clinical research field.
Cell alignment plays a crucial role in the repair and regeneration of tissues, which is caused by the "contact guidance" of micro/nano structures. In this paper, the nano-grooves with 200 nm in width, 400 nm in period and 75 nm in depth were fabricated on gold substrate with the technique of nanoimprint to simulate the extracellular matrix (ECM). Electric cell-substrate impedance sensing (ECIS) was employed firstly to real-time monitor cell alignment of human foreskin fibroblasts (HFF) and human immortal keratinocyte cells (HaCaT) on nano-grooves, which are two important functional cell types in skin wound-healing. The cell images displayed that the nano-grooves could induce the alignment of HFF cells, in which, the cell arrangement along the direction of nano-grooves occurred prior to the cell elongation. While the nano-grooves couldn't influence the morphology of HaCaT cells, and their adhesion and spread were delayed. In the ECIS monitoring, HFF and HaCaT cells both presented increased normalized impedance (NI) values at their respective characteristic frequencies of 977 and 1465 Hz on nano-grooves and flat electrodes with the prolongation of culture time during 24 h and the increasing trends of NI values were also similar:in the first 6 h, NI values increased faster, and then, the increasing rates declined obviously. HFF cells on nano-grooves generated more intense impedance signals with a larger distinction of increasing rate than those on flat electrodes, indicating that the nano-grooves could promote the adhesion and spread of HFF cells and the directional arrangement had a larger impact on the variation of NI values than cell elongation. While HFF cells adhered and spread in random directions, leading to the reduced difference in increasing rate of NI values. The NI values of HFF cells was further correlated with cell alignment, showing the enhanced impedance responses with the rising percentage of aligned cells. More importantly, there was a good linear correlation between NI values and the percentage of cells arranging along the direction of nano-grooves. In contrast, HaCaT cells had smaller NI values on the nano-grooves with the similar increasing rates, compared to the flat electrodes, revealing that the nano-grooves were less suitable for the adhesion and spread of HaCaT cells with almost no change of cell morphology, and the cell adhesion could cause more obvious variation of NI values than cell spread. Our research would provide a support for the development of complex cell sensors based on ECIS and its application in clinical research field.
2017, 75(11): 1121-1125
doi: 10.6023/A17060271
Abstract:
For proteins' diverse range of structural and functional features, they are important populations of biomolecules within organisms. Common methods to detect proteins are with the help of fluorescence or enzyme. Due to the advantages like lable-free and single-molecule detection, nanopore technology provides a novel platform for proteins' characterization. In this experiment, the patch clamp amplifier is used to apply the voltage and acquire the tiny current blockage. The Si3N4 membrane drilled with a nanopore separated the buffer solution into two sides:cis and trans. When the voltage applied into the buffer solution, charged proteins would been driven through the pore from one side to the other. Then, a series of current blockages could be obtained. By analysing these data, the size and conformation of the biomolecules could be acquired. In this paper, we using solid-state nanopore detected single protein and protein-protein complexes. The nanopore was characterized firstly. Then, both the applied voltage and the pH of the electrolyte solution were regulated. Under the low voltage, the sample proteins could be regarded as a rigid spheroid, and the dwell time is decreased with the voltage increasing. It was found that, the charges carried by proteins could be improved by higher pH of buffer solution, so that the dwell time would been shortened. Furthermore, based on the high specific between the antigen and antibody which are proteins, the translocation events before and after the addition of specific antigen into the solution with antibody were compared. Results showed that the relative current drop of the complex is larger than the pure antibody, implying that the antigen has been bound into the antibody. Due to the difference of excluded volume, the antibody and antigen-antibody complexes could be distinguished by the solid-state nanopore. In the future, the nanopore technology is promising to be applied into the recognition of multiply proteins and protein-protein interaction.
For proteins' diverse range of structural and functional features, they are important populations of biomolecules within organisms. Common methods to detect proteins are with the help of fluorescence or enzyme. Due to the advantages like lable-free and single-molecule detection, nanopore technology provides a novel platform for proteins' characterization. In this experiment, the patch clamp amplifier is used to apply the voltage and acquire the tiny current blockage. The Si3N4 membrane drilled with a nanopore separated the buffer solution into two sides:cis and trans. When the voltage applied into the buffer solution, charged proteins would been driven through the pore from one side to the other. Then, a series of current blockages could be obtained. By analysing these data, the size and conformation of the biomolecules could be acquired. In this paper, we using solid-state nanopore detected single protein and protein-protein complexes. The nanopore was characterized firstly. Then, both the applied voltage and the pH of the electrolyte solution were regulated. Under the low voltage, the sample proteins could be regarded as a rigid spheroid, and the dwell time is decreased with the voltage increasing. It was found that, the charges carried by proteins could be improved by higher pH of buffer solution, so that the dwell time would been shortened. Furthermore, based on the high specific between the antigen and antibody which are proteins, the translocation events before and after the addition of specific antigen into the solution with antibody were compared. Results showed that the relative current drop of the complex is larger than the pure antibody, implying that the antigen has been bound into the antibody. Due to the difference of excluded volume, the antibody and antigen-antibody complexes could be distinguished by the solid-state nanopore. In the future, the nanopore technology is promising to be applied into the recognition of multiply proteins and protein-protein interaction.
