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The present study develops a rapid, simple and efficient method for the determination of type IV collagenase by using a specific peptide-modified quartz crystal microbalance (QCM). A small peptide (P1), contains a specific sequence (Pro-Gly) and a terminal cysteine, was synthetized and immobilized to the surface of QCM electrode via the reaction between Au and thiol of the cysteine. The peptide bond between proline and glycine can be specific hydrolyzed cleavage by type IV collagenase, which enabled the modified electrode with a high selectivity toward type IV collagenase. The cleaving process caused a frequency change of QCM to give a signal related to the concentration of type IV collagenase. The morphologies of the modified electrodes were characterized by scanning electron microscope (SEM) and the specific hydrolyzed cleavage process was monitored by QCM. When P1 was modified with gold nanoparticles (P1-Au NPs), the signal could be amplified to further enhance the sensitivity of the designed sensor due to the high-mass of the modified Au NPs. Compared the direct unamplified assay, the values obtained for the limit of detection for type IV collagenase was 0.96 ng mL-1, yielding about 6.5 times of magnitude improvement in sensitivity. This signal enhanced peptide based QCM biosensor for type IV collagenase also showed good selectivity and sensitivity in complex matrix.

In this work, a nonenzymatic electrochemical sensor based on electrochemical water splitting-assisted electrocatalysis is developed for wearable perspiration glucose analysis. Pd nanoparticles (Pd NPs) encapsulated in a Co-based zeolitic imidazolate framework (ZIF-67) is prepared and used as the electrocatalyst. In comparison to previously reported nonenzymatic glucose sensors which detect glucose in alkaline buffers, the proposed sensor analyzes glucose under physiological pH with no additional reagents, which enables wearable, maintenance-free perspiration glucose monitoring for a long time. The nonenzymatic sensor and a flexible printed circuit board (FPCB) is integrated into a sweatband for real-time analysis of perspiration glucose. The test results of perspiration glucose using our sensor are correlated to those of blood glucose tests by a commercial glucose meter. The sensitivity of the sensor remains stable within 2 months when it is stored unpacked under ambient conditions. Therefore, we believe it is promising for wearable nonenzymatic glucose monitoring for noninvasive clinical analysis and sport applications.

One of the most critical problems of point-of-care testing is how to reduce the interference of background, especially under resource-limited conditions when sample pretreatment is not available. In this work we report a potentiometric method for point-of-care testing with minimum background. The method is based on the principles of a concentration cell which is a type of galvanic cells. It is an electrochemical cell having two carbon electrodes. The potential of each electrode is determined by ratio of a redox couple (i.e. Fe(CN)64−/3-) on the electrode surface. On one electrode, the adsorbed enzyme catalyzes the oxidation of analyte by Fe(CN)63− which produces Fe(CN)64−. The shift of the potential was because of the analyte as well as the background. In the other channel, no enzyme was present so that the shift of the potential, if any, is owing to the background. By measuring the potential difference between the two electrodes (i.e. voltage of the concentration cell), analyte can be quantitatively determined with most of the background eliminated. As the proof-of-concept analyte, blood glucose is quantitatively detected using a voltammeter with acceptable selectivity and accuracy. Noble metal electrodes that are indispensable for conventional electrochemical sensing are not required. All these features simplify the fabrication procedure and reduce the cost for the detection. Therefore, we believe it is promising for electrochemical point-of-care testing.

A novel label-free strategy for the detection of bacteria was developed by using a specific antimicrobial peptide (AMP)-functionalized quartz crystal microbalance (QCM) electrode. This electrode interface was successfully applied to detect pathogenic Escherichia coli O157:H7 based on the specific affinity between the small synthetic antimicrobial peptide and the bacterial cell of pathogenic E. coli O157:H7. The concentrations of pathogenic E. coli O157:H7 were sensitively measured by the frequency response of the QCM with a detection limit of 0.4 cfu μL(-1). The detection can be fulfilled within 10 min because it does not require germiculture process. On the other hand, if the specific antimicrobial peptides were immobilized on a gold electrode, this label-free strategy can also be performed by electrochemical impedance spectroscopy (EIS). Compared with QCM technique, the EIS measurement gives a lower sensitivity and needs a longer assay time. The combination of antimicrobial peptides with the real-time responses of QCM, as well as electronic read-out monitoring of EIS, may open a new way for the direct detection of bacteria.

A simple two-step method was employed for preparing nano-sized gold nanoparticles-graphene composite to construct a GNPs-GR-SDS modified electrode. Hemoglobin (Hb) was successfully immobilized on the surface of a basal plane graphite (BPG) electrode through a simple dropping technique. Direct electrochemistry and electrocatalysis of the hemoglobin-modified electrode was investigated. The as-prepared composites showed an obvious promotion of the direct electro-transfer between hemoglobin and the electrode. A couple of well-defined and quasi-reversible Hb CV peaks can be observed in a phosphate buffer solution (pH 7.0). The separation of anodic and cathodic peak potentials is 81 mV, indicating a fast electron transfer reaction. The experimental results also clarified that the immobilized Hb retained its biological activity for the catalysis toward NO. The biosensor showed high sensitivity and fast response upon the addition of NO, under the conditions of pH 7.0, potential -0.82 V. The time to reach the stable-state current was less than 3 s, and the linear response range of NO was 0.72-7.92 μM, with a correlation coefficient of 0.9991.

The interaction of aqua (N-salicylideneglycinato)copper(II) (Cu(salgly)2+) complex with calf thymus DNA has been investigated by cyclic voltammetry. Potential-modulated DNA cleavage in the presence of Cu(salgly)2+ complex was performed at a gold electrode in a thin layer cell. DNA can be efficiently cleaved by electrochemically reducing Cu(salgly)2+ complex to Cu(salgly)+ complex at -0.7 V (vs. Ag/AgCl). When the solution was aerated with a small flow of O2 during electrolysis, the extent of DNA cleavage was dramatically enhanced, and hydroxyl radical scavengers inhibited DNA cleavage. These results suggested that O2 and hydroxyl radical were involved in potential-modulated DNA cleavage reaction. The percentage of DNA cleavage was enhanced as the working potential was shifted to more negative values and the electrolysis time was increased. It was also dependent on the ratio of Cu(salgly)2+ complex to DNA concentration. The cleaved DNA fragments were separated by high performance liquid chromatography (HPLC). The experimental results indicated that the method for potential-modulated DNA cleavage by Cu(salgly)2+ complex was simple and efficient.

alpha-Fe(2)O(3) nanoparticles prepared using a simple solution-combusting method have been dispersed in chitosan (CH) solution to fabricate nanocomposite film on glass carbon electrode (GCE). The as-prepared alpha-Fe(2)O(3) nanoparticles were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM). The nanocomposite film exhibits high electrocatalytic oxidation for nitric oxide (NO) and reduction for hydrogen peroxide (H(2)O(2)). The electrocatalytic oxidation peak is observed at +0.82 V (vs. Ag/AgCl) and controlled by diffusion process. The electrocatalytic reduction peak is observed at -0.45 V (vs. Ag/AgCl) and controlled by diffusion process. This alpha-Fe(2)O(3)-CH/GCE nanocomposite bioelectrode has response time of 5 s, linearity as 5.0 x 10(-7) to 15.0 x 10(-6) M of NO with a detection limit of 8.0 x 10(-8) M and a sensitivity of -283.6 microA/mM. This alpha-Fe(2)O(3)-CH/GCE nanocomposite bioelectrode was further utilized in detection of H(2)O(2) with a detection limit of 4.0 x 10(-7) M, linearity as 1.0 x 10(-6) to 44.0 x 10(-6) M and with a sensitivity of 21.62 microA/mM. The shelf life of this bioelectrode is about 6 weeks under room temperature conditions.

Direct electron transfer between Cytochrome c (Cyt.c) and electrode can be achieved through immobilizing Cyt.c on the surface of multi-walled carbon nanotubes (MWNTs). Under the condition of cyclic potential scans, Cyt.c can be adsorbed on the surface of MWNTs that were modified on a glassy carbon (GC) electrode to form an approximate monolayer. The redox characteristic and bioactivity of Cyt.c could be remained after it was adsorbed on MWNTs' surface. This provides a way to construct a new biosenser based on the activity of Cyt.c. Further investigation displayed that Cyt.c adsorbed on MWNTs showed an enzyme-like activity to catalyze the reduction of nitric oxide (NO). Due to catalyzing by Cyt.c, the reduction of NO in aqueous solution was achieved, which reductive potential appeared at -0.747V (vs. SCE). The peak currents were linearly proportional to concentration of NO in the range from 2 to 48 micromol/l with a limit of detection of 1.3 microM. The biosensor showed a good stability and excellent repeatability.

The acid-treated multi-walled carbon nanotubes (MWNTs), which were modified on the surface of gold electrode, offers substantial improvements in voltammetric sensitivity and selectivity towards the determination of dopamine (DA). It can inhibit the voltammetric response of ascorbic acid (AA) while the redox reaction of dopamine is promoted. When a differential pulse voltammetric (DPV) technique was used, the peak separation between DAs and AAs was 244 mV. Based on this, a selective method could be constructed to detect DA in the presence of 1,000 times higher concentration of AA. The effect of various experimental parameters on the voltammetric response of dopamine was investigated. Under the chosen conditions, the peak currents are correspondent linearly to the concentrations of DA in the range of 5 x 10(-7) approximately 4 x 10(-4) mol L(-1) with a limit of detection of 2 x 10(-7) mol L(-1). The proposed method can be applied to detect DA in real samples.

A quartz crystal microbalance (QCM) biosensor for theophylline was developed by recognition of RNA aptamer and gold nanoparticle amplification technique. Firstly, a designed small single-stranded RNA, RNA1, was immobilized onto the QCM electrode through a thiol linker. Then, the complementary stranded RNA2, which can combine with RNA1 to form a double-stranded RNA with a recognition unit of theophylline, could be self-assembled on the QCM electrode surface through a hybrid reaction in the presence of theophylline. The recognition process could cause a frequency change of QCM to give the signal related to theophylline. When RNA2 was tethered to gold nanoparticles, the signal could be amplified to further enhance the sensitivity of the designed sensor. Under the optimal conditions, the QCM-based biosensor showed excellent sensitivity (limit of detection, 8.2 nM) and specificity with a dissociation constant of Kd = 5.26 × 10(-7) M. The sensor can be used to quantitatively detect theophylline in serum, suggesting that it can be applied in complex biological samples.