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A reduced graphene oxide-based enzyme-modified field-effect transistor (RGO-EnFET) was fabricated to study the enzymatic kinetics between acetylcholinesterase (AChE) and acetylcholine (ACh), which are related to the progression and treatment of Alzheimer’s disease (AD). The RGO-EnFET exhibited typical ambipolar transfer characteristics with a charge neutrality point (the Dirac point, V Dirac ) in an aqueous environment, and biological events occurring on the RGO surface were evaluated by observing the Dirac point shift (Δ V Dirac ) according to reactions. First, the pH sensitivity of the RGO-EnFET was measured to be 24.12 mV pH −1 for a pH range of 4–10 with excellent repeatability. Then, ACh quantification in the concentration range of 1 μM–10 mM was evaluated, with a linear slope of 13.9 mV dec −1 being obtained between Δ V Dirac and the ACh concentration on a logarithmic scale. The effects of AChE inhibitors (donepezil and rivastigmine) on the AChE enzymatic activity were also investigated. The distinguishable inhibition rates were acquired for donepezil and rivastigmine at saturation levels of 90% and 75%, respectively. These results indicate that the RGO-EnFET biosensor was successfully exploited as an in vitro analytical tool and has potential of future application in the study of enzymatic kinetics and drug screening for therapeutic purposes. [ABSTRACT FROM AUTHOR]

Ion concentration polarization (ICP) preconcentration is a pretreatment method that is actively utilized in the analysis of low-abundance biomolecules. In biofluids (e.g. urine, sweat, blood, serum, plasma, saliva, etc.), low-concentrated target analytes presented among large number of background molecules under a high ionic concentration, there still exist several hurdles in the utilization of ICP preconcentration in the such high ionic fluids. This is especially true in the case of blood-based biofluids, such as plasma and serum, wherein on account of the abundance biomolecules as well as high ionic buffer concentration makes the ICP preconcentration process difficult to realize. In this study, we have demonstrated the realization of ICP preconcentration of blood-based biofluids (serum) using a paper-based preconcentrator. We acquired preconcentration factors (PF) for 25.5, 127.5 and 255 mM of human serum were 40, 10, and 5.5 within 20 min. The squared fluorescence intensity is also found to be inversely proportional to ionic concentration, showing that the PF are strongly correlated to the Debye length of the buffer solution. Using the paper-based preconcentrator, we were able to acquire effective preconcentration factor (PF eff ) of 5.17, 4.88, 4.58, and 4.23 for the 1X, 0.75X, 0.5X, and 0.1X diluted solutions, demonstrating approximately 5 times increase in PF eff for all prepared human serum samples. [ABSTRACT FROM AUTHOR]