Growth of AgI semiconductors on tailored 3D porous Ti3C2 MXene/graphene oxide aerogel to develop sensitive and selective "signal-on" photoelectrochemical sensor for H2S determination

Signal amplification strategies in photoelectrochemical sensing of carcinoembryonic antigen

Early detection of cancer markers is critical for cancer diagnosis and cancer therapy since these markers may indicate cancer risk, incidence, and disease prognosis. Carcinoembryonic antigen (CEA) is a type of non-specific and broad-spectrum cancer biomarker commonly utilized for early cancer diagnosis. Moreover, it serves as an essential tool to assess the efficacy of cancer treatment and monitor tumor recurrence as well as metastasis, thus garnering significant attention for precise and sensitive CEA detection. In recent years, photoelectrochemical (PEC) techniques have emerged as prominent methods in CEA detection due to the advantages of PEC, such as simple equipment requirements, cost-effectiveness, high sensitivity, low interference from background signals, and easy of instrument miniaturization. Different signal amplification methods have been reported in PEC sensors for CEA analysis. Based on these, this article reviews PEC sensors based on various signal amplification strategies for detection of CEA during the last five years. The advantages and drawbacks of these sensors were discussed, as well as future challenges.

Recent insights on MXene-based architectures for monitoring and sensing of gaseous pollutants: A review

Epidemiology and public health concerns have primarily relied on the accurate control of gas pollutants, requiring highly efficient gas sensor devices for detecting hazardous gases. Despite the dedication of many efforts in this era, the precise, continuous scrutiny of gases remains elusive for appropriate gas selectivity, prompt response and recovery time, proper repeatability, as well as low cost. Accordingly, nanostructured architectural sensing cues have received enormous attention toward versatile detection and sensing procedures. As a representational nanostructure, the MXene family has been widely introduced to tailor and augment sensor patterns by providing large surface area, tunable surface chemistry, superior electrical conductivity, chemical stability, compatibility with flexible substrates, and potential for multifunctionality. Additionally, they could be synthesized in various formations of film and layered designs, fibrous membranes, and gel-like structures, creating synergetic effects that can provide superior gas-sensing performance. Herein, the synthesis and benefits of MXene nanosheets as gas-sensitive materials, in tandem with the past-to-present progress of MXene-based gas sensors in the formation of films, fibrous, and gel-like configurations, are comprehensively reviewed. As an in-depth reference, the present overview could shed light on further advancing gas sensor architectures developed based on MXene structures.

In Situ Synthesis of Hierarchical Co(CO3)0.5(OH)·0.11H2O@ZIF-67/WO3 With High Humidity Immunity and Response to H2S Sensing

H2S gas sensors with facile preparation, low detection limits, and high selectivity are crucial for environmental and human health monitoring. However, it is difficult to maintain a high response of H2S gas sensors under high humidity in practical applications. To face this dilemma, a layer-by-layer growth method is applied to in situ prepare a nanostructured Co(CO3)0.5(OH)·0.11H2O/WO3 coated by a hydrophobic hierarchical ZIF-67 as the H2S sensor. This novel composite exhibits excellent humidity immunity without sacrificing the excellent sensitivity and selectivity of H2S. At a low operating temperature of 90 °C, a remarkable response value of 1052.3 to 100 ppm H2S has been achieved, which is 779 and 9.36 times higher than that of pure WO3 and Co(CO3)0.5(OH)·0.11H2O/WO3, respectively. More importantly, an 82.2% relative response value remains at a high humidity of 75%RH. The sensing mechanisms are investigated using gas chromatography-mass spectrometry (GC-MS), which revealed that the reaction products are H2O and SO2. The high humidity immunity and fast response of the Co(CO3)0.5(OH)·0.11H2O@ZIF-67/WO3 demonstrate the layer-by-layer in situ synthesis method holds the potential application for the development of high-performance WO3-based H2S sensors.

A hydrogen sulfide photoelectrochemical sensor based on BiVO4/Fe2O3 heterojunction

A BiVO4/Fe2O3 heterojunction for non-enzymatic photoelectrochemical (PEC) determination of hydrogen sulfide (H2S) is reported. The BiVO4/Fe2O3 heterojunction promoted the separation of photo-generated carriers, reduced electron-hole recombination, and thus improved electron collection and photocurrent. The proposed BiVO4/Fe2O3/FTO sensor exhibited a linear range of 1-500 μM and a detection limit of 0.51 nM H2S. In addition, high selectivity, good reproducibility, and stability were obtained for H2S sensing. The detection of H2S in water and serum samples demonstrated its feasibility. This work provides a new strategy to detect and understand the bio-function of H2S in the biological environment.

Carbon-based photoelectrochemical sensors: recent developments and future prospects

Owing to the considerable potential of photoelectrochemical (PEC) sensors, they have gained significant attention in the analysis of biological, environmental, and food markers. However, the limited charge mass transfer efficiency and rapid recombination of electron hole pairs have become obstacles in the development of PEC sensors. In this case, considering the unique advantages of carbon-based materials, they can be used as photosensitizers, supporting materials and conductive substrates and coupled with semiconductors to prepare composite materials, solving the above problems. In addition, there are many types of carbon materials, which can have semiconductor properties and form heterojunctions after coupling with semiconductors, effectively promoting the separation of electron hole pairs. Herein, we aimed to provide a comprehensive analysis of reports on carbon-based PEC sensors by introducing their research and application status and discussing future development trends in this field. In particular, the types and performance improvement strategies of carbon-based electrodes and the working principles of carbon-based PEC sensors are explained. Furthermore, the applications of carbon-based photoelectric sensors in environmental monitoring, biomedicine, and food detection are highlighted. Finally, the current limitations in the research on carbon-based PEC sensors are emphasized and the need to enhance the sensitivity and selectivity through material modification, structural design, improved device performance, and other strategies are emphasized.

Electrochemical microfluidic immunosensor with graphene-decorated gold nanoporous for T-2 mycotoxin detection

T-2 is one of the most potent cytotoxic food-borne mycotoxins. In this work, we have developed and characterized an electrochemical microfluidic immunosensor for T-2 toxin quantification in wheat germ samples. T-2 toxin detection was carried out using a competitive immunoassay method based on monoclonal anti-T-2 antibodies immobilized on the poly(methyl methacrylate) (PMMA) microfluidic central channel. The platinum wire working electrode at the end of the channel was in situ modified by a single-step electrodeposition procedure with reduced graphene oxide (rGO)-nanoporous gold (NPG). T-2 toxin in the sample was allowed to compete with T-2-horseradish peroxidase (HRP) conjugated for the specific recognizing sites of immobilized anti-T-2 monoclonal antibodies. The HRP, in the presence of hydrogen peroxide (H2O2), catalyzes the oxidation of 4-tert-butylcatechol (4-TBC), whose back electrochemical reduction was detected on the nanostructured electrode at -0.15 V. Thus, at low T-2 concentrations in the sample, more enzymatically conjugated T-2 will bind to the capture antibodies, and, therefore, a higher current is expected. The detection limits found for electrochemical immunosensor, and commercial ELISA procedure were 0.10 μg kg-1 and 10 μg kg-1, and the intra- and inter-assay coefficients of variation were below 5.35% and 6.87%, respectively. Finally, our microfluidic immunosensor to T-2 toxin will significantly contribute to faster, direct, and secure in situ analysis in agricultural samples.

Construction of smartphone-adapted signal visualization platform for dual-mode detection of H2S based on integrated metal-organic framework nanoprobes

Hydrogen sulfide (H2S) is a toxic contaminant and has great influence on many physiological processes. Due to various pathophysiological roles and environmental pollution problems, it is necessary to construct and develop simple and portable monitoring sensors for the precise detection of H2S. Herein, we developed a smartphone-adapted dual-mode detection platform by integrating the colorimetric and photothermal imaging analysis into a metal-organic framework-based chip (ZIF-8/Cu). Due to the nanoconfinement effect of ZIF-8, small-sized plasmonic CuS could be in-situ formed during the detection procedure of H2S and endowed the chips with excellent photothermal properties. By constructing a smartphone-adapted photothermal imager, the metal-organic framework-based chip could achieve a portable photothermal imaging analysis of H2S. Moreover, as the formed CuS was a good peroxidase-like nanozyme, the chips could also be used to trigger the enzymic catalytic reaction toward the chromogenic reaction of 3,3',5,5'-tetramethylbenzidine (TMB)-H2O2, thus providing another colorimetric sensing mode by using a smartphone App. In this smartphone-adapted visualization platform, the portable chemosensors could simultaneously achieve double detection modes at one electrode, which provided a new pathway for the accurate detection of H2S and circumvented the false-positive or negative errors during the detection process. Besides, by using the finite difference time domain (FDTD) simulation method, the in-depth mechanism, including the plasmonic effect and spatial electromagnetic field distribution, was explored to provide a possible reason for the excellent sensing performance of the dual-mode visualization platform. This work provides a new insight into the construction of the accurate, portable and smart sensing platform in the visual screening of H2S.

Split-type photoelectrochemical immunoassay for sensitive quantification of carcinoembryonic antigen based on target-induced in situ formation of Z-type heterojunction

Carcinoembryonic antigen (CEA), a vital biomarker, plays a significant role in the early diagnosis and prognostic estimation of malignant tumors. In this study, a split-type photoelectrochemical immunoassay for the sensitive quantification of CEA has been successfully developed based on the target-induced in situ formation of a Z-type heterojunction. First, gold nanoparticle-decorated ZnIn2S4 (AuNPs/ZnIn2S4) composites were synthesized and used for the fabrication of photoelectrodes. Then, the detection antibody labeled with Ag nanoparticles was formed and applied for the biorecognition of CEA and subsequent liberation of Ag+ ions to induce the in situ formation of Ag2S/AuNPs/ZnIn2S4, a Z-type heterojunction, on the photoelectrode. The Z-type Ag2S/AuNPs/ZnIn2S4 heterojunction with effectively promoted separation of photogenerated charge carriers could lead to a markedly enhanced photocurrent response and highly sensitive quantification of CEA. Moreover, the three-dimensional spatial structure of ZnIn2S4 provides abundant active sites for the reaction and exhibits non-enzymatic properties, which are conducive to the further improvement of the analytical performance of CEA. The developed split-type photoelectrochemical immunoassay with good sensitivity, satisfactory selectivity, reliable stability, wide dynamic linear range (0.01-20 ng mL-1), and low detection limit (7.3 pg mL-1) offers valuable insights into the development of novel PEC biosensing models for the detection of tumor biomarkers and holds potential application value in the field of disease diagnosis.

Recent advances in photoelectrochemical platforms based on porous materials for environmental pollutant detection

Human health and ecology are seriously threatened by harmful environmental contaminants. It is essential to develop efficient and simple methods for their detection. Environmental pollutants can be detected using photoelectrochemical (PEC) detection technologies. The key ingredient in the PEC sensing system is the photoactive material. Due to the unique characteristics, such as a large surface area, enhanced exposure of active sites, and effective mass capture and diffusion, porous materials have been regarded as ideal sensing materials for the construction of PEC sensors. Extensive efforts have been devoted to the development and modification of PEC sensors based on porous materials. However, a review of the relationship between detection performance and the structure of porous materials is still lacking. In this work, we present an overview of PEC sensors based on porous materials. A number of typical porous materials are introduced separately, and their applications in PEC detection of different types of environmental pollutants are also discussed. More importantly, special attention has been paid to how the porous material's structure affects aspects like sensitivity, selectivity, and detection limits of the associated PEC sensor. In addition, future research perspectives in the area of PEC sensors based on porous materials are presented.

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.

Methyl orange as a novel colorimetric iodide indicator with in situ generation of H2O2 by etching uncoated Ag-Ti3C2 nanohybrids

Iodine intake remains a major public health concern, as both iodine excess and deficiency are related to adverse effects on health. Therefore, developing simple and economical methods to detect I^- is still in great demand. Herein, we constructed a visual I^- sensing platform based on the uncoated Ag-Ti₃C₂ nanohybrids using methyl orange (MO) as a colorimetric indicator. Plasmonic nanostructures are frequently employed in colorimetric analysis, but uncoated Ag nanoparticles (NPs) are unstable because their surface energies are usually high. Considering that Ag NPs can be etched by I^- via forming Ag-I bond, we introduce Ag-Ti₃C₂ nanohybrids because uncoated Ag NPs with immaculate surfaces are more conducive to binding with I^- and being etched. Dissolved O₂ molecules adsorbed on Ti³⁺ of Ti₃C₂ MXenes enable the in situ generation of H₂O₂ by iodine-etching of uncoated Ag-Ti₃C₂ nanohybrids. ∙OH radicals promote the degradation of MO through a self-driven Fenton-like process, exhibiting the color variation from orange to transparent. Under optimal conditions, the absorbance of MO at 465 nm decreases linearly with the concentration of I^- in the range of 0.5-300 μM, with a limit of detection as low as 0.31 μM. This work opens the feasibility of iodine-etching of Ag in developing novel probes for facile colorimetric determination of I^-.