A dual-photoelectrode photofuel cell based self-powered aptasensor using a multimeter as a direct visual readout strategy

Portable self-powered electrochemical aptasensor for ultrasensitive and real-time detection of microcystin-RR based on hydrovoltaic-photothermal coupling effect

Coupling different energy harvesting technologies to obtain an excellent output signal is essential for the development of high-performance self-powered electrochemical sensors. Herein, a novel hydrovoltaic-photothermal coupling self-powered electrochemical aptasensing platform was designed for sensitive detection of microcystin (MC-RR) with a digital multimeter as a direct visual readout strategy. The straightforward ultrasonic method was employed to synthesize polyaniline (PANI) and bismuth oxybromide (BiOBr) nanosheets, which were then integrated as active components in a hydrovoltaic device. The unique layer structure of two-dimensional (2D) nanomaterials BiOBr can create flexible interlayer spaces to accommodate various ions and water molecules, which was beneficial to construct evaporation-driven channels. Meanwhile, the exceptional photothermal characteristics of polyaniline could accelerate the water evaporation rate, consequently boosting the migration speed of charge carriers and increasing output signal. Moreover, a digital multimeter was connected to the constructed sensor for real-time displaying the output signal. With the assistance of aptamer, a novel self-powered electrochemical aptasensing platform was constructed for sensitive detection of MC-RR. Under optimum conditions, the output signal of the hydrovoltaic-photothermal coupling cell was linearly related to the logarithm of MC-RR concentration in the range of 1 fM to 1 nM with a detection limit of 0.31 fM (S/N = 3). Furthermore, this sensor also exhibited many advantages such as high selectivity, good repeatability and portability. Such novel strategy not only offers a completely new general approach to construct high-performance self-powered devices for the detection of MC-RR, but also provides a new strategy for advancing the miniaturization and field application of self-powered electrochemical sensors.

A bulit-in self-calibration ratiometric self-powered photoelectrochemical sensor for high-precision and sensitive detection of microcystin-RR

A novel high-precision aptasensor of microcystin-RR (MC-RR) is developed based on a ratiometric self-powered photoelectrochemical platform. In detail, the defective MoS2/Ti3C2 nanocomposite with good photoelectric activity was designed to serve as the photoanode of the sensor for enhancing the signal and improving the detection sensitivity. In order to effectively eliminate external interferences, the key point of this ratiometric device is the introduction of the spatial-resolved technique, which includes the detection section and the reference section, generating reference signals and response signals, respectively. Moreover, output power was used as the detection signal, instead of the traditional photocurrent or photovoltage. Further, potassium persulfate was introduced as electron acceptor, which was beneficial for improving the electron transport efficiency, hindering electron-hole recombination, and significantly promoting the performance of the sensor. Finally, aptamer was adopted as recognition element to capture MC-RR molecules. The prepared sensor had a linear range from 10-12 to 10-6 M, and the detection limit was 5.6 × 10-13 M (S/N = 3). It has good precision, selectivity, and sensitivity, which shows great prospects in the on-site accurate analysis of samples with high energy output in the self-powered sensing field.

A Photoelectrochemical Sensor for Real-Time Monitoring of Neurochemical Signals in the Brain of Awake Animals

Metal ion homeostasis is imperative for normal functioning of the brain. Considering the close association between brain metal ions and various pathological processes in brain diseases, it becomes essential to track their dynamics in awake animals for accurate physiological insights. Although ion-selective microelectrodes (ISMEs) have demonstrated great advantage in recording ion signals in awake animals, their intrinsic potential drift impairs their accuracy in long-term in vivo analysis. This study addresses the challenge by integrating ISMEs with photoelectrochemical (PEC) sensing, presenting an excitation-detection separated PEC platform based on potential regulation of ISMEs. A flexible indium tin oxide (Flex-ITO) electrode, modified with MoS2 nanosheets and Au NPs, serves as the photoelectrode and is integrated with a micro-LED. The integrated photoelectrode is placed on the rat skull to remain unaffected by animal activity. The potential of ISME dependent on the concentration of target K+ serves as the modulator of the photocurrent signal of the photoelectrode. The proposed design allows deep brain detection while minimizing interference with neurons, thus enabling real-time monitoring of neurochemical signals in awake animals. It successfully monitors changes in extracellular K+ levels in the rat brain after exposure to PM2.5, presenting a valuable analytical tool for understanding the impact of environmental factors on the nervous system.

Recent Trends in Self-Powered Photoelectrochemical Sensors: From the Perspective of Signal Output

Revolutionary developments in analytical chemistry have led to the rapid development of self-powered photoelectrochemical (PEC) sensors. Different from conventional PEC sensors, self-powered PEC sensors do not require an external power source or complex devices for the sensitive detection of targets. As a result, these sensors have enormous application potential for the development of novel portable sensors. An increasing body of work is making excellent progress toward the implementation of self-powered PEC sensors for detection, but there have been no reviews to date. The present review first introduces the state of the art in the development of self-powered PEC sensors. Then, different types of self-powered PEC sensors are summarized and discussed in detail, including their current, power, and potential. Additionally, single- and dual-photoelectrode systems are classified and systematically compared. Finally, the current developments and major challenges that need to be addressed are also summarized. This review provides valuable insights into the current state of self-powered PEC sensors to promote further progress in this field.

An ultrasensitive photo-driven self-powered aptasensor for microcystin-RR assay based on ZnIn2S4/Ti3C2 MXenes integrated with a matching capacitor for multiple signal amplification

A photo-driven self-powered aptasensor was constructed based on a matching capacitor and the ZnIn2S4/Ti3C2 heterojunction as the photoanode and Cu2O as the photocathode in a dual-photoelectrode sensing matrix for multiple signal amplification for the ultrasensitive detection of microcystin-RR (MC-RR). The introduction of Ti3C2 MXene nanosheets on the photoanode surface can not only accelerate the transfer and separation of photoinduced electron/hole pairs, thus enhancing the output signal of the photo-driven self-powered system, but also provide a larger specific surface area for the immobilization of the bio-recognition unit aptamer. More importantly, for a portable and miniaturized device, a micro-workstation with the size of a universal serial bus (USB) disk and a novel short-circuit current access was proposed to capture the instantaneous output electrical signal for real-time data tracking. In such a way, a sensitivity of 2.7 mA pM-1 was achieved when the matching capacitor was integrated into the self-powered system, which was 22 times that without a capacitor. After the interaction between MC-RR and the corresponding aptamer, a 'signal-off' detection configuration was formed via the steric hindrance effect. Therefore, such a multiple signal amplification system realized the ultrasensitive and selective determination of MC-RR successfully. Under optimal conditions, the linear range of the self-powered aptasensor was 0.1 to 100 pM and the detection limit was 0.033 pM (S/N = 3). The aptasensor was applied to the detection of MC-RR in fish, exhibiting good reproducibility (≈3.88%), paving the way for detecting microcystins in real-life samples.

A dual-photoelectrode fuel cell-driven self-powered aptasensor based on the 1D/2D In2S3/MoS2@Fe-CNTs heterojunction for the ultrasensitive detection of Staphylococcus aureus

A novel dual-electrode photo-fuel cell (PFC)-driven self-powered aptasensor was manufactured for the sensitive and selective detection of Staphylococcus aureus (S. aureus) using the one-dimensional (1D)/2D Schottky heterojunction comprising bimetallic indium/molybdenum sulfide nanosheets and iron-doped carbon nanotube (Fe-CNT) (denoted as In₂S₃/MoS₂@Fe-CNTs) as the photocathode. Given the generation of a robust interface at In₂S₃/MoS₂ and Fe-CNTs, the charge separation and transfer ability of photoexcited electron-hole pairs were enforced, thus improving the output voltage of the assembled PFC. In addition, the numerous active sites of the 1D/2D In₂S₃/MoS₂@Fe-CNTs Schottky heterojunction enabled the immobilization of large amounts of aptamer. Accordingly, the proposed PFC-driven self-powered aptasensor exhibited a wide linear range in 10-1 × 10⁷ CFU mL^-1 with a detection limit of 1.2 CFU mL^-1 toward S. aureus. High selectivity, excellent reproducibility, good stability, and acceptable regenerability, as well as great potential practicality, were also achieved for the detection of S. aureus using the developed PFC-driven self-powered aptasensor. This work not only provides a new photoactive material based on a robust 1D/2D Schottky heterojunction, but also constructs a novel PFC-based self-powered aptasensing strategy based on dual-photoelectrodes and with satisfactory performance for the detection of foodborne pathogens in diverse environments.

Photo-assisted Zn-air battery-driven self-powered aptasensor based on the 2D/2D Schottky heterojunction of cadmium-doped molybdenum disulfide and Ti3C2Tx nanosheets for the sensitive detection of penicillin G

A novel photocatalyzed Zn-air battery-driven (ZAB)-based aptasensor has been manufactured using the two dimensional (2D)/2D Schottky heterojunction as photocathode and Zn plate as photoanode. It was then employed to sensitively and selectively detect penicillin G (PG) in the complex environment. The 2D/2D Schottky heterojunction was established by the in situ growth of cadmium-doped molybdenum disulfide nanosheets (Cd-MoS₂ NSs) around Ti₃C₂T_x NSs (denoted as Cd-MoS₂@Ti₃C₂T_x) by using phosphomolybdic acid (PMo₁₂) as precursor, thioacetamide as sulfur source, and Cd(NO₃)₂ as a doping agent through the hydrothermal method. The gained Cd-MoS₂@Ti₃C₂T_x heterojunction possessed contact interface, hierarchical structure, and plenty of sulfur and oxygen vacancies, thus showing the enhanced separation ability of photocarriers and electron transfer. Due to the enhanced UV-vis light adsorption ability, high photoelectric conversion efficiency, and exposed catalytic active sites, the constructed photocatalyzed ZAB displayed a boosted output voltage of 1.43 V under UV-vis light irradiation. The developed ZAB-driven self-powered aptasensor demonstrated an ultralow detection limit of 0.06 fg mL^-1 within a PG concentration ranged from 1.0 fg mL^-1 to 0.1 ng mL^-1, as deduced from the power density-current curves, along with high specificity, good stability and promising reproducibility, as well as excellent regeneration ability and wide applicability. The present work provided an alternative analysis method for the sensitive analysis of antibiotics based on the portable photocatalyzed ZAB-driven self-powered aptasensor.

In Vivo Tracking of Persistent Organic Pollutants via a Coaxially Integrated and Implanted Photofuel Microsensor

In vivo tracking of persistent organic pollutants (POPs) is of great significance for assessing their risks to the ecological environment and human health. However, existing in vivo POPs detection methods are limited by the lethal sampling of living organisms, complex sample preparation processes, or bulky testing equipment. Photoelectrochemical (PEC) sensing with the merits of high sensitivity and simple equipment is a fast-developed method for in vivo analysis. A major obstacle for in vivo PEC sensors is the separated implantation of multiple electrodes and a light source, which raises concerns like multielectrode biofouling and electroactive molecules interference in the complex environment, uncertain electrode implant distance, and multiple insertion operations. Here, a coaxially implanted photofuel microsensor was developed by hiding the optical fiber-based photoanode inside the glass capillary-based biocathode, and the model target PCB77 can be detected with an ultralow detection limit (2.8 fg/mL). This unique photoanode-biocathode-light source integrated structure ensures excellent selectivity, good antifouling ability and biocompatibility, high accuracy, and less implant mechanical damage. Combined with a handheld pH meter, our sensor achieved convenient and direct tracking of the bioaccumulation levels of PCB77 in freely swimming fish.

Zinc vacancy mediated electron-hole separation in ZnO nanorod arrays for high-sensitivity organic photoelectrochemical transistor aptasensor

A novel strong solvent coordination leaching method was developed to prepare surface zinc vacancies in ZnO nanorod arrays. Remarkably, the surface-zinc-vacancy-rich ZnO nanorod arrays exhibit high electron-hole separation efficiency and excellent photoelectrochemical performance for use as a promising candidate for the next generation of organic photoelectrochemical transistor aptasensors.

Zinc-Air Battery-Based Self-Powered Sensor with High Output Power for Ultrasensitive MicroRNA let-7a Detection in Cancer Cells

Self-powered sensors do not require a power supply and are easy to miniaturize, which have potential for constructing wearable, portable, and real-time detection devices. However, it is challenging for the detection of low abundant targets due to the low output power density of fuel cells and much interference of complex biological environment. Herein, a new kind of photocatalytic zinc-air battery-based self-powered electrochemical sensor (ZAB-SPES) was constructed for the detection of microRNA let-7a (miRNA let-7a) by combining magnetic nanobeads (MBs) with a metal-organic framework loaded with glucose oxidase (MOFs@GOX). Poly(1,4-di(2-thienyl))benzene (PDTB) was used as the photocathode material, and the proposed ZAB-SPES had a high power density of 22.8 μW/cm², which was 2-3-fold of commonly used photofuel cells. MBs can capture and separate miRNA from complex samples quickly with a high separation efficiency of 99% within 60 s. The competitive reaction of oxygen reduction reaction between PDTB and MOFs@GOX would change the output power density of the ZAB-SPES. Based on the relationship between output power density and target concentration, the ZAB-SPES realized ultrasensitive detection of miRNA let-7a with a detection limit down to 1.38 fM. Furthermore, the successful detection of miRNA let-7a in A549 cancer cells indicated the great prospects of ZAB-SPES in clinical analysis and early diagnosis of cancers.