Recent Advances in Enzymatic Biofuel Cells to Power Up Wearable and Implantable Biosensors

Enzymatic biofuel cells (EBFCs) have emerged as a transformative solution in the quest for sustainable energy, offering a biocatalyst-driven alternative for powering wearable and implantable self-powered biosensors. These systems harness renewable enzyme activity under mild conditions, positioning them as ideal candidates for next-generation biosensing applications. Despite their promise, their practical deployment is limited by challenges such as low power density, restricted operational lifespan, and miniaturization complexities. This review provides an in-depth exploration of the evolving landscape of EBFC technology, beginning with fundamental principles and the latest developments in electron transfer mechanisms. A critical assessment of enzyme immobilization techniques, including physical adsorption, covalent binding, entrapment, and cross-linking, underscores the importance of optimizing enzyme stability and catalytic activity for enhanced bioelectrode performance. Additionally, we examine advanced bioelectrode materials, focusing on the role of nanostructures such as carbon-based nanomaterials, noble metals, conducting polymers, and metal-organic frameworks in improving electron transfer and boosting biosensor efficiency. Also, this review includes case studies of EBFCs in wearable self-powered biosensors, with particular attention to the real-time monitoring of neurotransmitters, glucose, lactate, and ethanol through sweat analysis, as well as their integration into implantable devices for continuous healthcare monitoring. Moreover, a dedicated discussion on challenges and trends highlights key limitations, including durability, power management, and scalability, while presenting innovative approaches to address these barriers. By addressing both technical and biological constraints, EBFCs hold the potential to revolutionize biomedical diagnostics and environmental monitoring, paving the way for highly efficient, autonomous biosensing platforms.

Self-powered biosensing platform for Highly sensitive detection of soluble CD44 protein

In this study, a self-powered biosensor based on an enzymatic biofuel cell was proposed for the first time for the ultrasensitive detection of soluble CD44 protein. The as-prepared biosensor was composed of the co-exist aptamer and glucose oxidase bioanode and bilirubin oxidase modified biocathode. Initially, the electron transfer from bioanode to biocathode was hindered due to the presence of the aptamer with high insulation, generating a low open-circuit voltage (EOCV). Once the target CD44 protein was present, it was recognized and captured by the aptamer at the bioanode, thus the interaction between the target CD44 protein and the immobilized aptamer caused the structural change at the surface of the electrode, which facilitated the transfer of electrons. The EOCV showed a good linear relationship with the logarithm of the CD44 protein concentrations in the range of 0.5-1000 ng mL-1 and the detection limit was 0.052 ng mL-1 (S/N = 3). The sensing platform showed excellent anti-interference performance and outstanding stability that maintained over 97% of original EOCV after 15 days. In addition, the relative standard deviation (1.40-1.96%) and recovery (100.23-101.31%) obtained from detecting CD44 protein in real-life blood samples without special pre-treatment indicated that the constructed biosensor had great potential for early cancer diagnosis.

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.

Competitive Assay for the Ultrasensitive Detection of Organophosphate Pesticides Based on a Fiber-Optic Particle Plasmon Resonance Biosensor and an Acetylcholinesterase Binding Peptide

An acetylcholinesterase (AChE) binding-based biosensor was developed for the ultrasensitive detection of organophosphate (OP) pesticides. The biosensor integrates the technique based on fiber-optic particle plasmon resonance detection and a synthetic AChE binding peptide conjugated with gold nanoparticles on the optical fiber surface via an AChE competitive binding assay. The OP pesticides present in the solution hinder the binding of AChE to the peptide on the biosensor by competing for the binding sites present in AChE. The limit of detection obtained for parathion using this method was observed to be 0.66 ppt (2.3 pM). This method shows a wide linear dynamic range of 6 orders. Furthermore, the use of the AChE binding peptide in the biosensor can better discriminate OPs against carbamates by using only a single biosensor. The practical application of this method was tested using spiked samples, which yielded good recovery and reproducibility. The spiked sample required minimal pretreatment before analysis; hence, this biosensor may also be used in the field.

Pesticide biosensors: trends and progresses

Pesticides, chemical substances extensively employed in agriculture to optimize crop yields, pose potential risks to human and environmental health. Consequently, regulatory frameworks are in place to restrict pesticide residue concentrations in water intended for human consumption. These regulations are implemented to safeguard consumer safety and mitigate any adverse effects on the environment and public health. Although gas chromatography- and liquid chromatography-mass spectrometry (GC-MS and LC-MS) are highly efficient techniques for pesticide quantification, their use is not suitable for real-time monitoring due to the need for sophisticated laboratory pretreatment of samples prior to analysis. Since they would enable analyte detection with selectivity and sensitivity without sample pretreatment, biosensors appear as a promising alternative. These consist of a bioreceptor allowing for specific recognition of the target and of a detection platform, which translates the biological interaction into a measurable signal. As early detection systems remain urgently needed to promptly alert and act in case of pollution, we review here the biosensors described in the literature for pesticide detection to advance their development for use in the field.

Antibody-free photoelectrochemical biosensor for DNA carboxylation detection based on SnS2@Ti3C2 heterojunction

As an important epigenetic modification, 5-carboxycytosine (5caC) played an important role in gene regulation, cell differentiation and growth. 5caC existed in many cells and tissues, but it was highly similar to the structure of other cytosine derivatives and had less content in the genome. Therefore, it was urgent to develop a sensitive and highly selective trace biosensor to detect 5caC. A novel photoelectrochemical biosensor was fabricated for 5-carboxy-2'-deoxycytidine-5'-triphosphate (5cadCTP) detection, where SnS₂@Ti₃C₂ nanocomposite was employed as photoactive material, polyethyleneimine was used as 5cadCTP recognition and capture reagent, and Ru(NH₃)₆³⁺ was used as photosensitizer for signal amplification. Due the good conductivity of Ti₃C₂ MXene and the matched energy band between Ti₃C₂ MXene and SnS₂, SnS₂@Ti₃C₂ nanocomposite presented strong photoactivity, which was beneficial to the high detection sensitivity. For specific recognition of 5cadCTP, the covalent interaction of -NH₂ in 5cadCTP with -COOH on the substrate electrode was used, which was beneficial to the high detection selectivity. A broad linear relationship between photocurrent and 5cadCTP concentration was observed ranging from 1 pM to 0.2 μM. The low detection limit of 260 fM was achieved. The developed method has high detection specificity and can even distinguish 5caC with its derivatives. In addition, the applicability was evaluated by detecting the content change of 5caC in the genomic DNA of rice seedlings after cultured with environmental pollutants. This work provides a novel platform for 5cadCTP detection, and it can also be applied to detect other cytosine derivatives with suitable recognition strategies.

A Direct Z-Scheme AgBr/CuBi2O4 Photocathode for Ultrasensitive Detection of Ciprofloxacin and Ofloxacin by Controlling the Release of Luminol in Self-Powered Microfluidic Photoelectrochemical Aptasensors

An innovative self-powered microfluidic photoelectrochemical (PEC) aptasensor was developed that uses photoactive AgBr/CuBi₂O₄ (ACO) composites as the photocathode matrix for ultrasensitive detection of ciprofloxacin (CIP) and ofloxacin (OFL). The formation of direct Z-scheme heterojunctions in ACO composites greatly aided electron/hole pair separation. Meanwhile, ZnIn₂S₄-decorated CdS nanorod arrays (CZIS) as the photoanode were used instead of a platinum counter electrode to provide electrons. The "signal-off" CIP detection was accomplished through the steric hindrance effect in the photoanode due to the combination of aptamer_(CIP) and CIP. To increase the cathodic photocurrent intensity for OFL determination, controlled release of luminol was first used. Luminol molecules were successfully embedded in the porous structure of silicon dioxide nanospheres (PSiO₂) by the electrostatic adsorption between PSiO₂ and aptamer_(OFL). The luminol released by specific recognition between OFL and aptamer_(OFL) could not only react with •O₂^- but also produce chemiluminescence emission, resulting in the "signal-on" state. Because of the signal "on-off-on", the proposed aptasensor exhibited wide linear ranges for CIP (0.001-100 ng/mL) and OFL (0.0005-100 ng/mL) detection. Furthermore, the low detection limits of CIP (0.06 pg/mL) and OFL (0.022 pg/mL) could achieve the ultrasensitive analysis.

Recent Advances in Potentiometric Biosensing

Potentiometric biosensors are incredibly versatile tools with budding uses in industry, security, environmental safety, and human health. This mini-review on recent (2018-2020) advances in the field of potentiometric biosensors is intended to give a general overview of the main types of potentiometric biosensors for novices while still providing a brief but thorough summary of the novel advances and trends for experienced practitioners. These trends include the incorporation of nanomaterials, graphene, and novel immobilization materials, as well as a strong push towards miniaturized, flexible, and self-powered devices for in-field or at-home use.

A photoelectrochemical sensor based on an acetylcholinesterase-CdS/ZnO-modified extended-gate field-effect transistor for glyphosate detection

A new photoelectrochemical enzyme biosensor based on an extended-gate field-effect transistor (EGFET) was constructed for the highly sensitive detection of glyphosate based on the inhibition of acetylcholinesterase (AChE) activity by glyphosate. First, a two-step hydrothermal method was used to introduce ZnO and CdS onto an activated indium tin oxide (ITO) electrode to prepare a CdS/ZnO/ITO electrode. Then, AChE was immobilized on CdS/ZnO/ITO with chitosan to obtain an AChE/CdS/ZnO EGFET sensor. Under optimal experimental conditions, the logarithmic value of glyphosate in the range of 1.0 × 10-15-1.0 × 10-11 mol L-1 exhibited a good linear relationship with the photo-drain current response. The detection limit was 3.8 × 10-16 mol L-1 (signal-to-noise ratio = 3). The results show that the AChE/CdS/ZnO EGFET sensor has extremely high sensitivity and good selectivity. Moreover, the sensor was used for the determination of glyphosate in vegetables, demonstrating its application for the real-time detection of samples.

Onsite/on-field analysis of pesticide and veterinary drug residues by a state-of-art technology: A review

Pesticides and veterinary drugs are generally employed to control pests and insects in crop and livestock farming. However, remaining residues are considered potentially hazardous to human health and the environment. Therefore, regular monitoring is required for assessing and legislation of pesticides and veterinary drugs. Various approaches to determining residues in various agricultural and animal food products have been reported. Most analytical methods involve sample extraction, purification (cleanup), and detection. Traditional sample preparation is time-consuming labor-intensive, expensive, and requires a large amount of toxic organic solvent, along with high probability for the decomposition of a compound before the analysis. Thus, modern sample preparation techniques, such as the quick, easy, cheap, effective, rugged, and safe method, have been widely accepted in the scientific community for its versatile application; however, it still requires a laboratory setup for the extraction and purification processes, which also involves the utilization of a toxic solvent. Therefore, it is crucial to elucidate recent technologies that are simple, portable, green, quick, and cost-effective for onsite and infield residue detections. Several technologies, such as surface-enhanced Raman spectroscopy, quantum dots, biosensing, and miniaturized gas chromatography, are now available. Further, several onsite techniques, such as ion mobility-mass spectrometry, are now being upgraded; some of them, although unable to analyze field sample directly, can analyze a large number of compounds within very short time (such as time-of-flight and Orbitrap mass spectrometry). Thus, to stay updated with scientific advances and analyze organic contaminants effectively and safely, it is necessary to study all of the state-of-art technology.

A Multiplexed Self-Powered Dual-Photoelectrode Biosensor for Detecting Dual Analytes Based on an Electron-Transfer-Regulated Conversion Strategy

Due to the inherent mechanism limitation of photocatalytic fuel cell based self-powered biosensors (PFC-SPBs), it was difficult to distinguish the power density of various photoactive materials or recognition events in one detection process, which made it lack multitarget quantitative capacity. In order to solve this problem, we proposed an electron-transfer-regulated conversion strategy for the construction of multiplexed PFC-SPBs. Herein, the n-type CdS/Fe₂O₃ nanorod array (NR) heterojunction and p-type CuBr semiconductor were used as photoactive materials to prepare the photoanode and photocathode. Based on the appropriate Fermi level differentiation between these two photoelectrodes, a self-powered sensing platform driven by visible light without external energy supply was achieved. In this design, two kinds of common and easily coexisting mycotoxins OTA and AFB1 acted as model analytes. The coupling of "signal off" and "signal on" was realized by controlling the electronic transmission on the interface between the photoanode and photocathode, so as to achieve the simultaneous detection of two mycotoxins. This work established a proof-of-concept for the integration of a dual-photoelectrode with dual-assay that could provide the innovative inspiration for the formation of a general multiplexed self-powered sensing platform.

Chemical-chemical redox cycling amplification strategy in a self-powered photoelectrochemical system: a proof of concept for signal amplified photocathodic immunoassay

A chemical-chemical redox cycling amplification strategy was introduced into a photocathodic immunosensing system. To prove the applicability of the method, a novel self-powered photochemical system by integrating the photoanode and photocathode was designed for protein analysis.

A photoelectrochemical biofuel cell based on a TiO2 nanotube array fluorine-doped tin oxide photoanode

Photoelectrochemical biofuel cells can convert light and chemical energy into electrical energy using a dye-sensitized titania (TiO2) fluorine-doped tin oxide photoanode and a platinum-coated fluorine-doped tin oxide cathode. TiO2 of the photoanode serves both as a support for dyes and as an electron-transporting medium, the structure of which can limit electron trapping and charge transporting and then affect the performance of the photoelectrochemical biofuel cells. TiO2 nanotube array films have been shown to enhance the efficiencies of both charge collection and electron injection, and hence a vertically aligned TiO2 nanotube array is investigated as a conductor for the tetrakis(4-carboxyphenyl)porphyrin dye to construct a new two-compartment photoelectrochemical biofuel cell. The photoelectrochemical biofuel cell containing the TiO2 nanotube array photoanode yields a short-circuit (Isc) current of 110 μA and an open-circuit (Voc) potential of 1010 mV. In contrast, the photovoltaic parameters, Isc and Voc of the photoelectrochemical biofuel cell with the mesoporous TiO2 nanocrystal fluorine-doped tin oxide photoanode, are 96.96 μA and 740 mV, respectively. Photovoltaic measurements show that the maximum incident photon-to-collected electron conversion efficiency was 58% at 430 nm through the spectral range (400–800 nm) for the photoelectrochemical biofuel cell with the TiO2 nanotube array fluorine-doped tin oxide photoanode. These results revealed that the TiO2 nanotube array had great potential for the photoelectrochemical biofuel cells.

Rolling circle amplification promoted magneto-controlled photoelectrochemical biosensor for organophosphorus pesticides based on dissolution of core-shell MnO2 nanoflower@CdS mediated by butyrylcholinesterase

A photoelectrochemical (PEC) aptasensing platform is devised for sensitive detection of an organophosphorus pesticide based on dissolution of core-shell MnO₂ nanoflower@CdS (MnO₂ NF@CdS) by thiocholine (TCh). TCH is produced from the butyrylcholinesterase-acetylthiocholine system, accompanied by target-triggered rolling circle amplification (RCA). The core-shell MnO₂ NF@CdS with excellent PEC performance was synthesized and employed as a photo-sensing platform. The target was detected on a functionalized magnetic probe with the corresponding aptamer. Upon malathion introduction, the aptamer was detached from the magnetic beads, while capture DNA (cDNA, with primer fragment) remained on the beads. The primer fragment in cDNA can trigger the RCA reaction to form a long single-stranded DNA (ssDNA). Furthermore, a large number of butyrylcholinesterase (BChE) were assembled on the long ssDNA strands through the hybridization with the S₂-Au-BChE probe. Thereafter, TCh generated from hydrolysis of ATCh by BChE can reduce MnO₂ NF (core) to Mn²⁺ and release the CdS nanoparticles (shell) from the platform electrode, significantly enhancing the PEC signal. Under optimal conditions, the proposed aptasensor exhibited high sensitivity for malathion with a low detection limit of 0.68 pg mL^-1. Meanwhile, it also presents outstanding specificity, reproducibility, and stability. Importantly, the sensing platform provides a new concept for detection of pesticide. Graphical abstract Herein, this work devised a photoelectrochemical (PEC) aptasensing platform for sensitive detection of organophosphorus pesticide based on dissolution of core-shell MnO₂ nanoflower@CdS (MnO₂ NF@CdS) by the as-produced thiocholine (TCh) from the butyrylcholinesterase-acetylthiocholine system, accompanying with the target-triggered rolling circle amplification (RCA).

Enhancement of Biosensors by Implementing Photoelectrochemical Processes

Research on biosensors is growing in relevance, taking benefit from groundbreaking knowledge that allows for new biosensing strategies. Electrochemical biosensors can benefit from research on semiconducting materials for energy applications. This research seeks the optimization of the semiconductor-electrode interfaces including light-harvesting materials, among other improvements. Once that knowledge is acquired, it can be implemented with biological recognition elements, which are able to transfer a chemical signal to the photoelectrochemical system, yielding photo-biosensors. This has been a matter of research as it allows both a superior suppression of background electrochemical signals and the switching ON and OFF upon illumination. Effective electrode-semiconductor interfaces and their coupling with biorecognition units are reviewed in this work.

Development of a near infrared novel bioimaging agent via co-oligomerization of Congo red with aniline and o-phenylenediamine: experimental and theoretical studies

With a view to study the effect of insertion of a multifunctional dye moiety on the photo physical properties of conducting polymers, the present paper reports for the first time the homopolymerization and co-oligomerization of Congo red (CR) dye with aniline and o-phenylenediamine. The co-oligomerization was established by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (1H-NMR), and ultraviolet-visible (UV-vis) spectroscopy while the morphology was examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The theoretical as well as experimental data of 1H-NMR as well as IR studies confirmed the co-oligomer formation while ultraviolet-visible spectroscopy studies revealed a dynamic change in the optical properties upon variation of co-oligomer composition. X-ray diffraction studies established a crystalline morphology of oligomers. Live cell confocal imaging studies revealed that the co-oligomers could be effectively used in NIR imaging.

Sensitive colorimetric sensor for point-of-care detection of acetylcholinesterase using cobalt oxyhydroxide nanoflakes

Point-of-care monitoring of acetylcholinesterase (AChE) is of significant importance for pesticide poisoning and disease diagnosis because it plays a pivotal role in biological nerve conduction systems. Herein, we designed a colorimetric strategy for the facile and accurate detection of AChE based on tandem catalysis with a multi-enzyme system, which is constituted by cobalt oxyhydroxide nanoflakes (CoOOH NFs) and choline oxidase (CHO). In this sensor, AChE catalytically hydrolyzed acetylcholine (ACh) to produce choline, which was further efficiently oxidized by CHO to yield H₂O₂. CoOOH NFs, as a nanozyme, efficiently catalyzed 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxTMB with the help of H₂O₂, accompanied by an enhancement of absorbance intensity. The resulting intensity could be employed as the signal output of the CHO/CoOOH/ACh system in monitoring AChE. Under optimal conditions, the developed sensor possessed a sensitive response to AChE with a detection limit of 33 μU mL^-1. Interestingly, the proposed platform was applied to fabricate a paper-based sensor for rapidly recognizing AChE by direct observation with the naked eyes. Combined with a smartphone and ImageJ software, we further developed an image-processing algorithm for the quantitative detection of AChE with highly promising results, which validated the outstanding potential of on-site application in clinical diagnostics and pesticide poisoning.