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In this work, we report the direct electrochemical oxidation of fentanyl using commercial screen-printed carbon electrodes (SPCEs) modified with carboxyl-functionalized carbon nanofibers (fCNFs). CNFs have surface chemistry and reactivity similar to carbon nanotubes (CNTs), yet they are easier to produce and are of a lower cost than CNTs. By monitoring the current produced during the electrochemical oxidation of fentanyl, variables such as fCNF loading, fentanyl accumulation time, electrolyte pH, and differential pulse voltammetry parameters were optimized. Under an optimized set of conditions, the fCNF/SPCEs responded linearly to fentanyl in the concentration range of 0.125-10 μM, with a limit of detection of 75 nM. The fCNF/SPCEs also demonstrated excellent selectivity against common cutting agents found in illicit drugs (e.g., glucose, sucrose, caffeine, acetaminophen, and theophylline) and interferents found in biological samples (e.g., ascorbic acid, NaCl, urea, creatinine, and uric acid). The performance of the sensor was also successfully tested using fentanyl spiked into an artificial urine sample. The straightforward electrode assembly process, low cost, ease of use, and rapid response make the fCNF/SPCEs prime candidates for the detection of fentanyl in both physiological samples and street drugs., Competing Interests: The authors declare no competing financial interest., (Crown © 2024. Published by American Chemical Society.)

The performance of redox-gated organic nonvolatile memory (NVM) based on conducting polymers was investigated by altering the polymer structure, composition, and local environment of three-terminal devices with a field-effect transistor (FET) geometry. The memory function was dependent on the presence of a redox active polymer with high conducting and low conducting states, the presence of a redox counter-reaction, and the ability to transport ions between the polymer and electrolyte phases. Simultaneous monitoring of both the "write" current and "readout" current revealed the switching dynamics of the devices and their dependence on the local atmosphere. Much faster and more durable response was observed in acetonitrile vapor than in a vacuum, indicating the importance of polar molecules for both ion motion and promotion of electrochemical reactions. The major factor determining "write" and "erase" speeds of redox-gated polymer memory devices was determined to be the rate of ion transport through the electrolyte layer to provide charge compensation for the conducting polarons in the active polymer layer. The results both confirm the mechanism of redox-gated memory action and identify the requirements of the conducting polymer, redox counter reaction, and electrolyte for practical applications as alternative solid-state nonvolatile memory devices.

A three terminal molecular memory device was monitored with in situ Raman spectroscopy during bias-induced switching between two metastable states having different conductivity. The device structure is similar to that of a polythiophene field effect transistor, but ethylviologen perchlorate was added to provide a redox counter-reaction to accompany polythiophene redox reactions. The conductivity of the polythiophene layer was reversibly switched between high and low conductance states with a "write/erase" (W/E) bias, while a separate readout circuit monitored the polymer conductance. Raman spectroscopy revealed reversible polythiophene oxidation to its polaron form accompanied by a one-electron viologen reduction. "Write", "read", and "erase" operations were repeatable, with only minor degradation of response after 200 W/E cycles. The devices exhibited switching immediately after fabrication and did not require an "electroforming" step required in many types of memory devices. Spatially resolved Raman spectroscopy revealed polaron formation throughout the polymer layer, even away from the electrodes in the channel and drain regions, indicating that thiophene oxidation "propagates" by growth of the conducting polaron form away from the source electrode. The results definitively demonstrate concurrent redox reactions of both polythiophene and viologen in solid-state devices and correlate such reactions with device conductivity. The mechanism deduced from spectroscopic and electronic monitoring should guide significant improvements in memory performance.

Spontaneous self-assembly of alkylthiosulfates on gold produce monolayers similar to the corresponding alkanethiols. Alkylthiosulfate self-assembly from THF solutions is inhibited in the presence of tetrabutylammonium tetrafluoroborate electrolyte. The mechanism of alkylthiosulfate self-assembly and the role of electrolyte and trace water in the solvent are investigated using open-circuit potential measurements, contact angle goniometry and redox electron transfer blocking experiments to explore the hypothesis that trace water present in the solvent facilitates monolayer formation on gold. Furthermore, the unique behavior of tetrabutylammonium tetrafluoroborate, compared to other tetrabutylammonium electrolytes, on the inhibition of alkylthiosulfate self-assembly has been explained.

Electrochemically directed self-assembly of alkylthiosulfates enables the selective formation of monolayers on gold surfaces. These monolayers are identical to those formed from the corresponding alkanethiols. However, the mechanistic details of monolayer formation under electrochemical conditions as well as the role of other variables and residual water in the solvent have not been extensively studied. A systematic investigation shows that self-assembly is not a result of an outer-sphere one-electron oxidation of alkylthiosulfate. Voltammetry and electrochemical quartz crystal microbalance techniques reveal that self-assembly involving alkylthiosulfates as well as alkanethiols under oxidative conditions proceed through direct reaction with gold oxide and in some cases is accompanied by corrosion. X-ray photoelectron spectroscopy indicates that monolayers can undergo rapid exchange with molecules in solution under electrochemically directed self-assembly conditions.