DJ-1,
a 20.7 kDa protein, is overexpressed in people who have bladder
cancer (BC). Its elevated concentration in urine allows it to serve
as a marker for BC. However, no biosensor for the detection of DJ-1
has been demonstrated. Here, we describe a virus bioresistor (VBR) capable of detecting DJ-1 in urine at a concentration
of 10 pM in 1 min. The VBR consists of a pair of
millimeter-scale gold electrodes that measure the electrical impedance
of an ultrathin (≈ 150–200 nm), two-layer polymeric
channel. The top layer of this channel (90–105 nm in thickness)
consists of an electrodeposited virus-PEDOT (PEDOT is poly(3,4-ethylenedioxythiophene))
composite containing embedded M13 virus particles that are engineered
to recognize and bind to the target protein of interest, DJ-1. The
bottom layer consists of spin-coated PEDOT–PSS (poly(styrenesulfonate)).
Together, these two layers constitute a current divider. We demonstrate
here that reducing the thickness of the bottom PEDOT–PSS layer
increases its resistance and concentrates the resistance drop of the
channel in the top virus-PEDOT layer, thereby increasing the sensitivity
of the VBR and enabling the detection of DJ-1. Large
signal amplitudes coupled with the inherent simplicity of the VBR sensor design result in high signal-to-noise (S/N > 100) and excellent sensor-to-sensor
reproducibility characterized by coefficients of variation in the
range of 3–7% across the DJ-1 binding curve down to a concentration
of 30 pM, near the 10 pM limit of detection (LOD), encompassing four
orders of magnitude in concentration.
A polymer-based electrode capable of specific detection of human serum albumin, and its glycated derivatives, is described. The sensor is constructed from a glass microscope slide coated with a synthesized, polythiophene film bearing a protected, iminodiacetic acid motif. The electrode surface is then further elaborated to a functional biosensor through deprotection of the iminodiacetic acid, followed by metal-affinity immobilization of a specific and high-affinity, albumin ligand. Albumin was then quantified in buffer and synthetic urine via electrochemical impedance spectroscopy. Glycated albumin was next bound to a boronic acid-modified, singlecysteine dihydrofolate reductase variant to quantify glycation ratios by square-wave voltammetry. The platform offers high sensitivity, specificity, and reproducibility in an inexpensive arrangement. The detection limits exceed the requirements for intermediate-term glycemic control monitoring in diabetes patients at 5 and 1 nM for albumin and its glycated forms, respectively.
Amperometric hydrogen peroxide enzyme inhibition biosensors based on horseradish peroxidase (HRP) immobilised on electropolymerised neutral red (NR) or directly on the surface of carbon film electrodes (CFE) have been successfully applied to the determination of toxic Cr(III) and Cr(VI). Parameters influencing the performance of the biosensor including the enzyme immobilisation method, the amount of hydrogen peroxide, applied potential and electrolyte pH were optimised. The inhibition of horseradish peroxidase by the chromium species was studied under the optimised conditions. Results from the quantitative analysis of chromium ions are discussed in terms of detection limit, linear range and sensitivity. The HRP kinetic interactions reveal mixed binding of Cr(III) with I50=3.8μM and inhibition binding constant Ki=11.3μM at HRP/PNR/CFE biosensors and uncompetitive binding of Cr(VI) with I50=3.9μM and Ki=0.78μM at HRP/CFE biosensors in the presence of H2O2 substrate. Interferences from other heavy metal ions were studied and the inhibition show very good selectivity towards Cr(III) and Cr(VI).
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