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To eliminate the interference effect of ascorbic acid (AA) and reduced nicotinamide adenine dinucleotide (NADH) on electrochemical detection of uric acid (UA), a non-enzymatic approach for electrochemical detection of UA was developed using the Nafion-modified screen-printed carbon electrode strip (SPCEs). Electrodeposition was utilized to control the thickness of Nafion film. With Nafion-modified SPCEs, the selectivity of UA from AA and NADH was investigated. The Nafion-modified SPCEs exhibits high selectivity of UA, good linearity, and reasonable detection limit in neutral pH environment. The interference effect can be evidently reduced. The advantages are no requirements of enzyme reagents, acid environment, and complicated preparation of the electrodes.

Screen-printed carbon electrode (SPCE) has been widely used in electrochemical (EC) field. Nevertheless, compared with some metal electrodes, SPCE is not sensitive to small amounts of reagent owing to its relatively low electron transfer rate. In this paper, the UV/ozone modification was proposed to treat SPCE to improve its electron transfer rate and EC performance. The changes of SPCE morphology and composition induced by UV/ozone modification were investigated in detail. The results show that the improved electron transfer rate can be mainly attributed to the increase of oxygen functional groups. To clarify the essential EC characterization, potentiodynamic polarization and electrochemical impedance spectroscopy of K3[Fe(CN)6] was studied. Furthermore, to demonstrate the improved EC effect, two typical samples: small-molecule K3[Fe(CN)6] and macro-molecule nicotinamide adenine dinucleotide (NADH), were measured by cyclic voltammetry. After UV/ozone modification, the oxidation potential and peak current responses to K3[Fe(CN)6] and NADH were obviously improved in both original and CNT-modified SPCEs. Whereas, the original SPCE is more suitable to measure macromolecule NADH rather than CNT-modified one as the oxidative products of NADH are more likely to adsorb on rough surface.

Due to unique advantages, carbon is widely used as electrode material for electrochemical sensors. In this paper, an efficient method of combining the electrohydrodynamic jet (E-jet) printing with the lift-off process was presented to produce the carbon-based three-electrode plate. The metal pattern was formed by lift-off process. Then the carbon pattern was printed on the metal layer by E-jet. Moreover, a graphene layer was printed on the carbon layer to improve the sensing performance by E-jet and the effect of scanning rate on thickness and density of layer was investigated. At last, an electrochemical sensor was developed with the well-made three-electrode plate and utilized to detect the samples of potassium ferricyanide and nicotinamide adenine dinucleotide. The results showed that a lower anodic peak potential was obtained in the graphene-modified carbon electrode than that of the bare carbon electrode. And in the electrochemical measurement of potassium ferricyanide, the graphene-modified electrode can decrease the potential distance between the anodic peak and the cathodic peak. It implied that the additional graphene-nanosheets can increase the reactive area and the capability of electronic conduction, thereby making the EC reaction easier to occur.

The activity of glutamic pyruvic transaminase (GPT) is an important clinical evidence for some acute diseases such as acute hepatopathy and myocardial infarction. Thus, there is a demand for rapid determination of GPT in small formats at point-of-need. Herein, we describe a novel method of electrochemical determination of GPT with microfluidic technique. GPT activity was indirectly determined via the electrochemical (EC) detection of nicotinamide adenine dinucleotide (NADH) produced from the GPT transdeamination reaction. A type of microfluidic chip was developed, in which a passive mixer comprising 100 sub-ribs and a three-electrode strip for EC were integrated. To verify the response to NADH, a series of NADH concentrations varying from 19 µM to 5 mM were calibrated with cyclic voltammetry within the microfluidic chip. And a linear relationship with R 2 0.9982 between the peak current and the concentration of NADH was obtained. Then, the GPT activity was determined using the chips containing and not containing a ribs-type mixer. And a linear relationship which contained two sections between the GPT activity and the peak current was obtained. The chip with a ribs-type mixer exhibited the sensitivity of 0.0341 μA U−1 L in the range of 10–50 U L−1 and 0.0236 μA U−1 L in the range of 50–250 U L−1. And the detection limit of the chip with a ribs-type mixer was 9.25 U L−1. The complete detection process of GPT activity within the microfluidic chip was realized, and the time-consuming problem was remarkably improved too.