A novel cathodic "signal-off" strategy was proposed for photoelectrochemical (PEC) aptasensing of oxytetracycline (OTC). The PEC sensor was constructed by employing a p-type semiconductor BiOI doped with graphene (G) as photoactive species and OTC-binding aptamer as a recognition element. The morphological structure and crystalline phases of obtained BiOI-G nanocomposites were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The UV-visible absorption spectroscopic analysis indicated that doping of BiOI with graphene improved the absorption of materials in the visible light region. Moreover, graphene could facilitate the electron transfer of BiOI modified electrode. As a result, the cathodic photocurrent response of BiOI under visible light irradiation was significantly promoted when a suitable amount of graphene was doped. When amine-functionalized OTC-binding aptamer was immobilized on the BiOI-G modified electrode, a cathodic PEC aptasensor was fabricated, which exhibited a declined photocurrent response to OTC. Under the optimized conditions, the photocurrent response of aptamer/BiOI-G/FTO was linearly proportional to the concentration of OTC ranging from 4.0 to 150 nM, with a detection limit (3S/N) of 0.9 nM. This novel PEC sensing strategy demonstrated an ultrasensitive method for OTC detection with high selectivity and good stability.

A self-powered sensing system possesses the capacity of harvesting energy from the environment and has no requirement for external electrical power supply during the chemical sensing of analytes. Herein, we design an enzyme-free self-powered sensing platform based on a photofuel cell (PFC) driven by visible-light, using glucose as a model analyte. The fabricated PFC consists of a Ni(OH)2/CdS/TiO2 photoanode and a hemin-graphene (HG) nanocomposite coated cathode in separated chambers. Under visible-light irradiation, glucose in the anodic chamber is facilely oxidized on Ni(OH)2/CdS/TiO2 while H2O2 in the cathodic chamber is catalytically reduced by HG, which generates a certain cell output sensitive to the variation of glucose concentration. Thus, a PFC based self-powered sensor is realized for glucose detection. Compared to the existing enzymatic self-powered glucose sensors, our proposed PFC based strategy exhibits much lower detection concentration. Moreover, it avoids the limitation of conventional enzyme immobilized electrodes and has the potential to develop high-performance self-powered sensors with broader analyte species.

A photocathode-based photocatalytic fuel cell (PFC) was fabricated and proposed as a self-powered sensor for p-nitrophenol (p-NP) detection. The PFC was comprised of a photocathode and an anode in separated chambers, which could generate suitable power output under photoirradiation to drive the sensing process. In this device, p-type PbS quantum dots-modified glass carbon electrode (GCE) served as the photocathode for the reduction of p-NP under photoirradiation while graphene-modified GCE was employed as the anode for the oxidation of ascorbic acid. In order to improve the selectivity of the PFC sensor, p-NP binding molecularly imprinted polymer (MIP) was introduced on the photocathode. Under optimal conditions, the open circuit voltage of the constructed PFC sensor was found to sensitively respond to p-NP in a wide concentration range from 0.05 μM to 20 μM. The proposed sensor exhibited high selectivity, good reproducibility, and stability, demonstrating the successful combination of MIP with photocathode in construction of high-performance PFC self-powered sensors for pollutant monitoring.

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