Electrochemically Active Thin Carbon Films with Enhanced Adhesion to Silicon Substrates.

Thin carbon films deposited on technologically relevant substrates, such as silicon wafers, can be easily implemented in miniaturized electrochemical devices and used for sensing applications. However, a major issue in most carbon films is the weak film/substrate adhesion that shortens the working device lifetime. This paper describes the facile preparation of robust thin carbon films on silicon substrates by one-pot sol-gel synthesis. The improved adherence of these carbon films is based on the incorporation of silica through the controlled synthesis of a resorcinol/formaldehyde gel modified with aminopropyltriethoxysilane. The films demonstrate excellent adhesion to the silicon substrate, good homogeneity, excellent electrical conductivity and superior electrochemical performance. Moreover, this approach opens the door to the fabrication of carbon thin-film electrodes by photolithographic techniques.

Cytochrome P450 2D6 based electrochemical sensor for the determination of codeine.

Considering the enzymatic activity of the cytochrome P450 2D6 on substrates such as codeine, the current paper includes the development of an enzymatic biosensor for detection of this drug. Home-made screen-printed electrodes were used as electrochemical transducers of the biosensor, in which the enzyme was covalently attached to the carbon surface of the working electrode, this type of modification being the most suitable for the immobilization of the biological element. Chronoamperometric measurements were carried out under optimum conditions of pH and working potential, pH 7 and +200 mV vs. screen-printed Ag/AgCl electrode, giving a reduction signal related to the concentration of codeine in solution. Consecutive additions of a solution of codeine were performed to obtain calibration curves in order to validate the electrochemical method in terms of precision and calculate its capability of detection. These biosensors were used for the determination of codeine in urine and commercial pharmaceutical samples.

Sensitive and selective cocaine electrochemical detection using disposable sensors.

This paper describes the voltammetric determination of cocaine in presence of three different interferences that could be found in street samples using disposable sensors. The electrochemical analysis of this alkaloid can be affected by the presence of codeine, paracetamol or caffeine, whose oxidation peaks may overlap and lead to false positives. This work describes two different solutions to this problem. On one hand, the modification of disposable carbon sensors with carbon nanotubes allows the voltammetric quantification of cocaine by using ordinary least squares regressions in the concentration range from 10 to 155 µmol L(-1), with a reproducibility of 5.6% (RSD, n = 7. On the other hand, partial least squares regressions are used for the resolution of the overlapped voltammetric signals when using screen-printed carbon electrodes without any modification. Both procedures have been successfully applied to the evaluation of the purity of cocaine street samples.

Electrochemical determination of cocaine using screen-printed cytochrome P450 2B4 based biosensors.

This paper describes the development of screen-printed cytochrome P450 2B4 based biosensors, from the fabrication of the device using a single screen-printing technology to its characterization and application in the determination of cocaine street samples. Voltammetric measurements were first performed in order to study the electrochemical behavior of the enzyme trapped in the structure of the working electrode, as well as its interaction with one of its substrates, cocaine. Then, chronoamperometric measurements were carried out for the characterization of the biosensors. Calibration curves under optimum conditions of the experimental variables have been used for establishing the reproducibility (5.91%, n=5), the repeatability (10.45%, n=3) and the capability of detection (0.2mM, α=ß=0.05) of the described method in the calibration range from 0.2 to 1.2mM. Finally, the performance of the developed biosensors has been successfully probed by the analysis of the purity of cocaine street samples.

Screen-printed biosensor based on the inhibition of the acetylcholinesterase activity for the determination of codeine.

The current paper presents the chronoamperometric determination of codeine using screen-printed carbon electrodes that incorporate tetrathiafulvalene in the matrix of the working electrode, as mediator, and cross-linked acetylcholinesterase. Applying a potential of +250 mV, a 1mM solution of acetylthiocholine in electrolyte solution pH 7 gives an oxidation signal due to the dimerization of its metabolite after the reaction with the enzyme. This electrochemical signal is decreased by consecutive additions of a solution of codeine, which allows the performance of curves of calibration for the validation of this electrochemical method, giving a reproducibility of 3.31% (n=6) and a capability of detection of 20 µM. This type of inhibition has been studied by means of a Lineweaver-Burk plot. Additionally, the developed biosensor was used for the determination of the quantity of codeine in pharmaceutical commercial tablets and urine samples.

CYP450 biosensors based on screen-printed carbon electrodes for the determination of cocaine.

A new electrochemical method has been described and characterized for the determination of cocaine using screen-printed biosensors. The enzyme cytochrome P450 was covalently attached to screen-printed carbon electrodes. Experimental design methodology has been performed to optimize the pH and the applied potential, both variables that have an influence on the chronoamperometric determination of the drug. This method showed a reproducibility of 3.56% (n=4) related to the slopes of the calibration curves performed in the range from 19 up to 166nM. It has been probed the used of this kind of biosensors in the determination of cocaine in street samples, with an average capability of detection of 23.05±3.53nM (n=3, α=ß=0.05).