Detection of the antiepileptic drug phenytoin using a single free-standing piezoresistive microcantilever for therapeutic drug monitoring.

Phenytoin, one of the most widely used antiepileptic drugs, suppresses the abnormal brain activity often seen in seizures. In this study, we report the electrical detection of phenytoin as an antiepileptic medication with a narrow therapeutic dosage range to which therapeutic drug monitoring (TDM) is applied. The measurement technique used an electrical detection of a piezoresistive microcantilever biosensor. This label-free, electrically measured microcantilever can be miniaturized in order to be portable for point-of-care, personal diagnosis or for personalized therapeutic drug monitoring. The miniaturized piezoresistive microcantilever was fabricated by micro-electro-mechanical system processes, and was integrated into a microfluidic channel with a system for label-free detection. The microcantilever biosensor was approved for the detection of phenytoin in solutions of deionized water and 100% fetal bovine serum. A linear profile in a drug-concentration range of 10-80 µg/mL was detected, with the signal resolution being about 0.005 Ω. The concentration sensitivity was 2.94×10(-6) (µg/mL)(-1). The binding affinity (KD) was calculated to be 58 µg/mL. The results of the present piezoresistive microcantilever biosensors showed a solid correlation of phenytoin drug detection with that in the clinically used fluorescence polarization immunoassay (FPIA).

Electrical detection of C-reactive protein using a single free-standing, thermally controlled piezoresistive microcantilever for highly reproducible and accurate measurements.

This study demonstrates a novel method for electrical detection of C-reactive protein (CRP) as a means of identifying an infection in the body, or as a cardiovascular disease risk assay. The method uses a single free-standing, thermally controlled piezoresistive microcantilever biosensor. In a commonly used sensing arrangement of conventional dual cantilevers in the Wheatstone bridge circuit, reference and gold-coated sensing cantilevers that inherently have heterogeneous surface materials and different multilayer structures may yield independent responses to the liquid environmental changes of chemical substances, flow field and temperature, leading to unwanted signal disturbance for biosensing targets. In this study, the single free-standing microcantilever for biosensing applications is employed to resolve the dual-beam problem of individual responses in chemical solutions and, in a thermally controlled system, to maintain its sensor performance due to the sensitive temperature effect. With this type of single temperature-controlled microcantilever sensor, the electrical detection of various CRP concentrations from 1 µg/mL to 200 µg/mL was performed, which covers the clinically relevant range. Induced surface stresses were measured at between 0.25 N/m and 3.4 N/m with high reproducibility. Moreover, the binding affinity (KD) of CRP and anti-CRP interaction was found to be 18.83 ± 2.99 µg/mL, which agreed with results in previous reported studies. This biosensing technique thus proves valuable in detecting inflammation, and in cardiovascular disease risk assays.