Huiren Xu

A novel label-free microfluidic paper-based immunosensor for highly sensitive electrochemical detection of carcinoembryonic antigen.

In this work, a highly sensitive label-free paper-based electrochemical immunosensor employing screen-printed working electrode (SPWE) for detection of carcinoembryonic antigen (CEA) was fabricated. In order to raise the detection sensitivity and immobilize anti-CEA, amino functional graphene (NH2-G)/thionine (Thi)/gold nanoparticles (AuNPs) nanocomposites were synthesized and coated on SPWE. The principle of the immunosensor determination was based on the fact that the decreased response currents of Thi were proportional to the concentrations of corresponding antigens due to the formation of antibody-antigen immunocomplex. Experimental results revealed that the immunoassay enabled the determination of standard CEA solutions with linear working ranges of 50pgmL(-1) to 500ngmL(-1), the limit of detections for CEA is 10pgmL(-1) (S/N=3) and its corresponding correlation coefficients were 0.996. Furthermore, the proposed immunosensor could be used for the determination of clinical serum samples. A large number of clinical serum samples were detected and the relative errors between measured values and reference concentrations were calculated. Results showed that this novel paper-based electrochemical immunosensor could provide a new platform for low cost, sensitive, specific, and point-of-care diagnosis in cancer detection.

Highly sensitive detection of quantal dopamine secretion from pheochromocytoma cells using neural microelectrode array electrodeposited with polypyrrole graphene.

For the measurement of events of dopamine (DA) release as well as the coordinating neurotransmission in the nerve system, a neural microelectrode array (nMEA) electrodeposited directionally with polypyrrole graphene (PG) nanocomposites was fabricated. The deposited graphene significantly increased the surface area of working electrode, which led to the nMEA (with diameter of 20 μm) with excellent selectivity and sensitivity to DA. Furthermore, PG film modification exhibited low detection limit (4 nM, S/N = 3.21), high sensitivity, and good linearity in the presence of ascorbic acid (e.g., 13933.12 μA mM(-1) cm(-2) in the range of 0.8-10 μM). In particular, the nMEA combined with the patch-clamp system was used to detect quantized DA release from pheochromocytoma cells under 100 mM K(+) stimulation. The nMEA that integrates 60 microelectrodes is novel for detecting a large number of samples simultaneously, which has potential for neural communication research.

A wireless point-of-care testing system for the detection of neuron-specific enolase with microfluidic paper-based analytical devices

Neuron-specific enolase (NSE) had clinical significance on diagnosis, staging, monitoring effect and judging prognosis of small cell lung cancer. Thus, there had a growing demand for the on-site testing of NSE. Here, a wireless point-of-care testing (POCT) system with electrochemical measurement for NSE detection was developed and verified. The wireless POCT system consisted of microfluidic paper-based analytical devices (μPADs), electrochemical detector and Androids smartphone. Differential pulse voltammetry (DPV) measurement was adopted by means of electrochemical detector which including a potentiostat and current-to-voltage converter. μPADs were modified with nanocomposites synthesized by Amino functional graphene, thionine and gold nanoparticles (NH2-G/Thi/AuNPs) as immunosensors for NSE detection. Combined with μPADs, the performance of the wireless POCT system was evaluated. The peak currents showed good linear relationship of the logarithm of NSE concentration ranging from 1 to 500ngmL-1 with the limit of detection (LOD) of 10pgmL-1. The detection results were automatically stored in EEPROM memory and could be displayed on Androids smartphone through Bluetooth in real time. The detection results were comparable to those measured by a commercial electrochemical workstation. The wireless POCT system had the potential for on-site testing of other tumor markers.

Selective recognition of 5-hydroxytryptamine and dopamine on a multi-walled carbon nanotube-chitosan hybrid film-modified microelectrode array.

It is difficult to determine dopamine (DA) and 5-hydroxytryptamine (5-HT) accurately because of the interference of ascorbic acid (AA) in vitro, which has a high concentration and can be oxidized at a potential close to DA and 5-HT at a conventional electrode, combined with the overlapping voltammetric signal of DA and 5-HT at a bare electrode. Herein, chitosan (CS) was used as a stabilizing matrix by electrochemical reaction, and multi-walled carbon nanotubes (MWCNTs) were modified onto the microelectrode array (MEA). The CS-MWCNT hybrid film-modified MEA was quite effective at simultaneously recognizing these species in a mixture and resolved the overlapping anodic peaks of AA, DA and 5-HT into three well-defined oxidation peaks in differential pulse voltammetry (DPV) at −80 mV, 105 mV and 300 mV (versus Ag|AgCl), respectively. The linear responses were obtained in the range of 5 × 10−6 M to 2 × 10−4 M for DA (r = 0.996) and in the range of 1 × 10−5 M to 3 × 10−4 M for 5-HT (r = 0.999) using the DPV under the presence of a single substance. While DA coexisted with 5-HT in the interference of 3 × 10−4 M AA, the linear responses were obtained in the range of 1 × 10−5 M to 3 × 10−4 M for selective molecular recognition of DA (r = 0.997) and 5-HT (r = 0.997) using the DPV. Therefore, this proposed MEA was successfully used for selective molecular recognition and determination of DA and 5-HT using the DPV, which has a potential application for real-time determination in vitro experiments.

Carbon fiber ultramicrodic electrode electrodeposited with over-oxidized polypyrrole for amperometric detection of vesicular exocytosis from pheochromocytoma cell.

Vesicular exocytosis is ubiquitous, but it is difficult to detect within the cells communication mechanism. For this purpose, a 2 μm ultramicrodic carbon fiber electrode was fabricated in this work based on electrodeposition with over-oxidized polypyrrole nanoparticle (PPyox-CFE), which was applied successfully for real-time monitoring of quantal exocytosis from individual pheochromocytoma (PC12) cells. PPyox-CFE was evaluated by dopamine (DA) solutions through cyclic voltammetry and amperometry electrochemical methods, and results revealed that PPyox-CFE improved the detection limit of DA. In particular, the sensitivity of DA was improved to 24.55 μA·μM−1·μm−2 using the PPyox-CFE. The ultramicrodic electrode combined with the patch-clamp system was used to detect vesicular exocytosis of DA from individual PC12 cells with 60 mM K+ stimulation. A total of 287 spikes released from 7 PC12 cells were statistically analyzed. The current amplitude (Imax) and the released charge (Q) of the amperometric spikes from the DA release by a stimulated PC12 cell is 45.1 ± 12.5 pA and 0.18 ± 0.04 pC, respectively. Furthermore, on average ∼562,000 molecules were released in each vesicular exocytosis. PPyox-CFE, with its capability of detecting vesicular exocytosis, has potential application in neuron communication research.

A high-sensitive nano-modified biosensor for dynamic monitoring of glutamate and neural spike covariation from rat cortex to hippocampal sub-regions

BACKGROUNDnHippocampus is a critical part of brain tissue involved in many cognitive neural activities. They are controlled by various neurotransmitters such as glutamate (Glu), and affected by electrophysiology.nnnNEW METHODnHerein, we fabricated a 16-site (25μm in diameter) microelectrode array (MEA) biosensor applied in dual-mode tests including Glu and neural spike measurements.nnnMETHODSnAll the 16 recording sites were electrodeposited with platinum nanoparticles (PtNPs) and 8 sites were used for electrical recording. Glutamate oxidase enzyme (Gluox) and 1,3-Phenylenediamine (mPD) layer were specially modified on the other 8 sites for Glu recording. The dual-mode MEA was implanted from cortex to hippocampus of anesthetized rat to record Glu content and firing rate.nnnRESULTSnThe electrical sites showed much lower impedance. The Glu sites showed much higher sensitivity(7.807 pA/μM), and ideal selectivity to the major molecules in brain. The post calibration sensitivity (3.935 pA/μM) maintained on a positive level. Different Glu content peaks including cortex (18.32μM) and hippocampal CA1 (4.39μM), CA3 (10.16μM), dentate gyrus (DG, two layers: 5.36μM and 10.34μM) have detected. The corresponded firing rate was recorded, too.nnnCOMPARISON WITH EXISTING METHODSnThis modification showed much lower impedance and much higher sensitivity. We obtained more neuron activities simultaneously by dual-mode recording. The covariation of Glu and neural spike signals was discovered in the specific hippocampus sub-region.nnnCONCLUSIONSnThe covariation between Glu and firing rate changes were synchronous, and effected by regions. The dual-mode signals were useful to find the neurology disease mechanism.

A Label-Free Microelectrode Array Based on One-Step Synthesis of Chitosan–Multi-Walled Carbon Nanotube–Thionine for Ultrasensitive Detection of Carcinoembryonic Antigen

Carcinoembryonic antigen (CEA) has been an extensively used tumor marker responsible for clinical early diagnosis of cervical carcinomas, and pancreatic, colorectal, gastric and lung cancer. Combined with micro-electro mechanical system (MEMS) technology, it is important to develop a novel immune microelectrode array (MEA) not only for rapid analysis of serum samples, but also for cell detection in vitro and in vivo. In this work, we depict a simple approach to modify chitosan–multi-walled carbon nanotubes–thionine (CS–MWCNTs–THI) hybrid film through one-step electrochemical deposition and the CS-MWCNTs-THI hybrid films are successfully employed to immobilize anti-CEA for fabricating simple, label-free, and highly sensitive electro-chemical immune MEAs. The detection principle of immune MEA was based on the fact that the increasing formation of the antigen-antibody immunocomplex resulted in the decreased response currents and the relationship between the current reductions with the corresponding CEA concentrations was directly proportional. Experimental results indicated that the label-free MEA had good selectivity and the limit of detection for CEA is 0.5 pg/mL signal to noise ratio (SNR) = 3. A linear calibration plot for the detection of CEA was obtained in a wide concentration range from 1 pg/mL to 100 ng/mL (r = 0.996). This novel MEA has potential applications for detecting CEA for the research on cancer cells and cancer tissue slices as well as for effective early diagnosis.

In Situ Real-Time Monitoring of Glutamate and Electrophysiology from Cortex to Hippocampus in Mice Based on a Microelectrode Array

Changes in the structure and function of the hippocampus contribute to epilepsy, schizophrenia and other neurological or mental disorders of the brain. Since the function of the hippocampus depends heavily on the glutamate (Glu) signaling pathways, in situ real-time detection of Glu neurotransmitter release and electrophysiological signals in hippocampus is of great significance. To achieve the dual-mode detection in mouse hippocampus in vivo, a 16-channel implantable microelectrode array (MEA) was fabricated by micro-electromechanical system (MEMS) technology. Twelve microelectrode sites were modified with platinum black for electrophysiological recording and four sites were modified with glutamate oxidase (GluOx) and 1,3-phenylenediamine (mPD) for selective electrochemical detection of Glu. The MEA was implanted from cortex to hippocampus in mouse brain for in situ real-time monitoring of Glu and electrophysiological signals. It was found that the Glu concentration in hippocampus was roughly 50 μM higher than that in the cortex, and the firing rate of concurrently recorded spikes declined from 6.32 ± 4.35 spikes/s in cortex to 0.09 ± 0.06 spikes/s in hippocampus. The present results demonstrated that the dual-mode MEA probe was capable in neurological detections in vivo with high spatial resolution and dynamical response, which lays the foundation for further pathology studies in the hippocampus of mouse models with nervous or mental disorders.

Label-free electrochemical detection of brain-derived neurotrophic factor based on a novel immune microelectrode array

Brain-derived neurotrophic factor (BDNF) has been shown to play an important role in numerous processes of functional and structural synaptic plasticity in the mammalian central nervous system. In this work, we report a novel immune microelectrode array (MEA) for electrochemical detection of BDNF without labeling step. The chitosan-thionine-multi-walled carbon nanotubes (CS-THI-MWCNTs) composite films as the bio-sensitive film are modified onto the MEA by electrochemical deposition and successfully adopted to immobilize anti-BDNF for the fabrication of electrochemical immune MEA. The THI acted as an electrochemical indicator for the immune response of BDNF. Due to surface-controlled process of THI redox reaction, the increasing formation of anti-BDNF-BDNF immunocomplex resulted in the decreased response currents of THI and the response currents were inversely proportional to the concentrations of corresponding BDNF. The test results of performance revealed that the label-free electrochemical immune MEA had a good stability, selectivity and the limit of detections for BDNF is 5 pg/mL. A linear calibration plot for detection of BDNF was obtained in a wide concentration range from 0.01 ng/mL to 100 ng/mL (r = 0.9995). This novel electrochemical immune MEA has potential applications to detect BDNF for neuroscience research.

Microelectrode arrays studies of glutamate excitatory pathway in hippocampus CA3 by offside KCl and glutamate stimulating

In our central nervous system (CNS), glutamate is an excitatory neurotransmitter that can be accumulated remarkably by brain tissue. As is noticeable from previous studies, glutamate is somehow closely related with most ways of normal and abnormal cerebral activities. It was significant to monitor glutamate concentration changes in vivo real time. Therefore, we developed an enzyme-based microelectrode array with high sensitivity (7.34pA/µM) and perfect linearity (R2=0.999). Selectivity to normal neurotransmitters satisfied our in vivo demands. Ultimately, we applied the electrode into the brain specific tissue to study glutamate excitatory pathway in hippocampus CA3 by offside KCl and glutamate stimulating. The hippocampus CA3 glutamate was detected about 18.17µM and 13.19µM by twice KCl stimulating in the offside cortex, and 6.50µM, 4.55µM by twice glutamate stimulating. All peak current back to the base level later. The self-regulation ability reflects the glutamate excitatory pathway from hippocampus CA3 to cortex.