Laser-Treated MXene as an Electrochemical Agent to Boost Properties of Semitransparent Photoelectrode Based on Titania Nanotubes.

In this study, Ti3C2Tx underwent laser treatment to reshape it, resulting in the formation of a TiO2/Ti3C2Tx heterojunction. The interaction with laser light induced the formation of spherical TiO2 composed of an anatase-rutile phase on the Ti3C2Tx surface. Such a heterostructure was loaded over a titania nanotube (TNT) layer, and the surface area was enhanced through immersion in a TiCl4 solution followed by thermal treatment. Consequently, the photon-to-electron conversion efficiency exhibits a 10-fold increase as compared to bare TNT. Moreover, for the sample produced with optimized conditions, five times higher photoactivity is observed in comparison to bare TNT. It was shown that under visible light irradiation the most photoactive heterojunction based on the tubular layer reveals a substantial drop in the charge transfer resistance of about 32% with respect to the dark condition. This can be attributed to the narrower band gaps of the modified material and improvement of the separation efficiency of the photogenerated electron-hole pairs. Overall results suggest that this investigation underscores TiO2/Ti3C2Tx as a promising noble-metal-free material that enhances both the electrochemical and photoelectrochemical performances of electrode materials based on TNT that can be further used in light-harvesting applications.

Electrochemically directed biofunctionalization of a lossy-mode resonance optical fiber sensor.

In this work, we present a direct electrochemical biofunctionalization of an indium-tin-oxide-coated lossy-mode resonance optical fiber sensor. The functionalization using a biotin derivative was performed by cyclic voltammetry in a 10 mM biotin hydrazide solution. All stages of the experiment were simultaneously verified with optical and electrochemical techniques. Performed measurements indicate the presence of a poly-biotin layer on the sensor's surface. Furthermore, dual-domain detection of 0.01 and 0.1 mg/mL of avidin confirms the sensor's viability for label-free detection.

Simultaneous optical and electrochemical label-free biosensing with ITO-coated lossy-mode resonance sensor.

In this work we discuss a new label-free biosensing device based on indium tin oxide (ITO) overlaid section of a multimode optical fiber fused silica core. The sensor has been used to optical measurements also simultaneously interrogated electrochemically (EC). Due to optimized thickness and optical properties of ITO film, a lossy-mode resonance (LMR) could be observed in the optical domain, where electrical properties of the film allowed for application of the sensor as a working electrode in an EC setup. It has been confirmed that the LMR response depends on optical properties of the external medium, as well as potential applied to the electrode during cyclic voltammetry. After the ITO surface functionalization with amine groups and covalently attached biotin, the device has been applied for label-free biosensing of avidin in both the domains simultaneously. On the example of biotin-avidin detection system it was demonstrated that when avidin concentration increases a decrease in current and increase in LMR wavelength shift were recorded in EC and optical domain, respectively. Both optical and EC responses follow the protein interaction process, and thus can be used as cross-verification of the readouts. Moreover, an extended information has been achieved comparing to solely EC interrogation, i.e., the grafting process of biotin and avidin was directly monitored optically displaying individual steps of an incubation procedure.

Optical Detection of Ketoprofen by Its Electropolymerization on an Indium Tin Oxide-Coated Optical Fiber Probe.

In this work an application of optical fiber sensors for real-time optical monitoring of electrochemical deposition of ketoprofen during its anodic oxidation is discussed. The sensors were fabricated by reactive magnetron sputtering of indium tin oxide (ITO) on a 2.5 cm-long core of polymer-clad silica fibers. ITO tuned in optical properties and thickness allows for achieving a lossy-mode resonance (LMR) phenomenon and it can be simultaneously applied as an electrode in an electrochemical setup. The ITO-LMR electrode allows for optical monitoring of changes occurring at the electrode during electrochemical processing. The studies have shown that the ITO-LMR sensor’s spectral response strongly depends on electrochemical modification of its surface by ketoprofen. The effect can be applied for real-time detection of ketoprofen. The obtained sensitivities reached over 1400 nm/M (nm·mg−1·L) and 16,400 a.u./M (a.u.·mg−1·L) for resonance wavelength and transmission shifts, respectively. The proposed method is a valuable alternative for the analysis of ketoprofen within the concentration range of 0.25⁻250 μg mL−1, and allows for its determination at therapeutic and toxic levels. The proposed novel sensing approach provides a promising strategy for both optical and electrochemical detection of electrochemical modifications of ITO or its surface by various compounds.