Nucleic acid-based wearable and implantable electrochemical sensors.

The rapid advancements in nucleic acid-based electrochemical sensors for implantable and wearable applications have marked a significant leap forward in the domain of personal healthcare over the last decade. This technology promises to revolutionize personalized healthcare by facilitating the early diagnosis of diseases, monitoring of disease progression, and tailoring of individual treatment plans. This review navigates through the latest developments in this field, focusing on the strategies for nucleic acid sensing that enable real-time and continuous biomarker analysis directly in various biofluids, such as blood, interstitial fluid, sweat, and saliva. The review delves into various nucleic acid sensing strategies, emphasizing the innovative designs of biorecognition elements and signal transduction mechanisms that enable implantable and wearable applications. Special perspective is given to enhance nucleic acid-based sensor selectivity and sensitivity, which are crucial for the accurate detection of low-level biomarkers. The integration of such sensors into implantable and wearable platforms, including microneedle arrays and flexible electronic systems, actualizes their use in on-body devices for health monitoring. We also tackle the technical challenges encountered in the development of these sensors, such as ensuring long-term stability, managing the complexity of biofluid dynamics, and fulfilling the need for real-time, continuous, and reagentless detection. In conclusion, the review highlights the importance of these sensors in the future of medical engineering, offering insights into design considerations and future research directions to overcome existing limitations and fully realize the potential of nucleic acid-based electrochemical sensors for healthcare applications.

Metal oxide hybridization enhances room temperature phosphorescence of carbon dots-SiO2 matrix for information encryption and anti-counterfeiting.

Room temperature phosphorescent (RTP) carbon dot (CD) materials have been widely used in various fields, but it is difficult to achieve a long lifetime, high stability and easy synthesis. In particular, realizing the phosphorescence emission of CDs using a metal oxide (MO) matrix is a challenge. Here, solid gels are synthesized via in situ hydrolysis, and then RTP CDs are synthesized based on a SiO2 matrix (CDs@SiO2) and hybridized with a MO matrix (CDs@SiO2-MO) by high-temperature calcination. Among the materials synthesized, Al2O3 matrix RTP CDs (CDs@SiO2-Al2O3) have a long phosphorescence lifetime of 689 ms and can exhibit yellow-green light visible to the naked eye for 9 s after the UV light (365 nm) is turned off. Compared with the green phosphorescence of CDs@SiO2, the yellow-green phosphorescence lifetime of CDs@SiO2-Al2O3 is enhanced by 420 ms. In addition, CDs@SiO2-Al2O3 maintains good stability of phosphorescence emission in water, strongly oxidizing solutions and organic solvents. As a result, CDs@SiO2-Al2O3 can be applied to the field of information encryption and security anti-counterfeiting, and this work provides a new, easy and efficient synthesis method for MO as an RTP CD matrix.

One-Step Preparation of High-Stability CsPbX3/CsPb2X5 Composite Microplates with Tunable Emission.

The core-shell structure is an effective means to improve the stability and optoelectronic properties of cesium lead halide (CsPbX3 (X = Cl, Br, I)) perovskite quantum dots (QDs). However, confined by the ionic radius differences, developing a core-shell packaging strategy suitable for the entire CsPbX3 system remains a challenge. In this study, we introduce an optimized hot-injection method for the epitaxial growth of the CsPb2X5 substrate on CsPbX3 surfaces, achieved by precisely controlling the reaction time and the ratio of lead halide precursors. The synthesized CsPbX3/CsPb2X5 composite microplates exhibit an emission light spectrum that covers the entire visible range. Crystallographic analyses and density functional theory (DFT) calculations reveal a minimal lattice mismatch between the (002) plane of CsPb2X5 and the (11¯0) plane of CsPbX3, facilitating the formation of high-quality type-I heterojunctions. Furthermore, introducing Cl- and I- significantly alters the surface energy of CsPb2X5's (110) plane, leading to an evolutionary morphological shift of grains from circular to square microplates. Benefiting from the passivation of CsPb2X5, the composites exhibit enhanced optical properties and stability. Subsequently, the white light-emitting diode prepared using the CsPbX3/CsPb2X5 composite microplates has a high luminescence efficiency of 136.76 lm/W and the PL intensity decays by only 3.6% after 24 h of continuous operation.

Stability Enhancement in All-Inorganic Perovskite Light Emitting Diodes via Dual Encapsulation.

Addressing the challenge of lighting stability in perovskite white light emitting diodes (WLEDs) is crucial for their commercial viability. CsPbX3 (X = Cl, Br, I, or mixed) nanocrystals (NCs) are promising for next-generation lighting due to their superior optical and electronic properties. However, the inherent soft material structure of CsPbX3 NCs is particularly susceptible to the elevated temperatures associated with prolonged WLED operation. Additionally, these NCs face stability challenges in high humidity environments, leading to reduced lighting performance. This study introduces a two-step dual encapsulation method, resulting in CsPbBr3@SiO2/Al2SiO5 composite fibers (CFs) with enhanced optical stability under extreme conditions. In testing, WLEDs incorporating these CFs, even under prolonged operation at high power (100 mA for 9 h), maintain consistent electroluminescence (EL) intensity and optoelectronic parameters, with surface temperatures reaching 84.2 °C. Crucially, when subjected to 85 °C and 85% relative humidity for 200 h, the WLEDs preserve 97% of their initial fluorescence efficiency. These findings underscore the efficacy of the dual encapsulation strategy in significantly improving perovskite material stability, marking a significant step toward their commercial application in optoelectronic lighting.

A wearable aptamer nanobiosensor for non-invasive female hormone monitoring.

Personalized monitoring of female hormones (for example, oestradiol) is of great interest in fertility and women's health. However, existing approaches usually require invasive blood draws and/or bulky analytical laboratory equipment, making them hard to implement at home. Here we report a skin-interfaced wearable aptamer nanobiosensor based on target-induced strand displacement for automatic and non-invasive monitoring of oestradiol via in situ sweat analysis. The reagentless, amplification-free and 'signal-on' detection approach coupled with a gold nanoparticle-MXene-based detection electrode offers extraordinary sensitivity with an ultra-low limit of detection of 0.14 pM. This fully integrated system is capable of autonomous sweat induction at rest via iontophoresis, precise microfluidic sweat sampling controlled via capillary bursting valves, real-time oestradiol analysis and calibration with simultaneously collected multivariate information (that is, temperature, pH and ionic strength), as well as signal processing and wireless communication with a user interface (for example, smartphone). We validated the technology in human participants. Our data indicate a cyclical fluctuation in sweat oestradiol during menstrual cycles, and a high correlation between sweat and blood oestradiol was identified. Our study opens up the potential for wearable sensors for non-invasive, personalized reproductive hormone monitoring.

Synergistic Enhancement of Near-Infrared Emission in CsPbCl3 Host via Co-Doping with Yb3+ and Nd3+ for Perovskite Light Emitting Diodes.

Perovskite nanocrystals (PeNCs) have emerged as a promising class of luminescent materials offering size and composition-tunable luminescence with high efficiency and color purity in the visible range. PeNCs doped with Yb3+ ions, known for their near-infrared (NIR) emission properties, have gained significant attention due to their potential applications. However, these materials still face challenges with weak NIR electroluminescence (EL) emission and low external quantum efficiency (EQE), primarily due to undesired resonance energy transfer (RET) occurring between the host and Yb3+ ions, which adversely affects their emission efficiency and device performance. Herein, we report the synergistic enhancement of NIR emission in a CsPbCl3 host through co-doping with Yb3+/Nd3+ ions for perovskite LEDs (PeLEDs). The co-doping of Yb3+/Nd3+ ions in a CsPbCl3 host resulted in enhanced NIR emission above 1000 nm, which is highly desirable for NIR optoelectronic applications. This cooperative energy transfer between Yb3+ and Nd3+ can enhance the overall efficiency of energy conversion. Furthermore, the PeLEDs incorporating the co-doped CsPbCl3/Yb3+/Nd3+ PeNCs as an emitting layer exhibited significantly enhanced NIR EL compared to the single doped PeLEDs. The optimized co-doped PeLEDs showed improved device performance, including increased EQE of 6.2% at 1035 nm wavelength and low turn-on voltage. Our findings highlight the potential of co-doping with Yb3+ and Nd3+ ions as a strategy for achieving synergistic enhancement of NIR emission in CsPbCl3 perovskite materials, which could pave the way for the development of highly efficient perovskite LEDs for NIR optoelectronic applications.

Ultrastable CsPbBr3@CsPb2Br5@TiO2 Composites for Photocatalytic and White Light-Emitting Diodes.

Although cesium halide lead (CsPbX3, X = Cl, Br, I) perovskite quantum dots (QDs) have excellent photovoltaic properties, their unstable characteristics are major limitations to application. Previous research has demonstrated that the core-shell structure can significantly improve the stability of CsPbX3 QDs and form heterojunctions at interfaces, enabling multifunctionalization of perovskite materials. In this article, we propose a convenient method to construct core-shell-structured perovskite materials, in which CsPbBr3@CsPb2Br5 core-shell micrometer crystals can be prepared by controlling the ratio of Cs+/Pb2+ in the precursor and the reaction time. The materials exhibited enhanced optical properties and stability that provided for further postprocessing. Subsequently, CsPbBr3@CsPb2Br5@TiO2 composites were obtained by coating a layer of dense TiO2 nanoparticles on the surfaces of micrometer crystals through hydrolysis of titanium precursors. According to density functional theory (DFT) calculations and experimental results, the presence of surface TiO2 promoted delocalization of photogenerated electrons and holes, enabling the CsPbBr3@CsPb2Br5@TiO2 composites to exhibit excellent performance in the field of photocatalysis. In addition, due to passivation of surface defects by CsPb2Br5 and TiO2 shells, the luminous intensity of white light-emitting diodes prepared with the materials only decayed by 2%-3% at high temperatures (>100 °C) when working for 24 h.

Studies on the optical stability of CsPbBr3 with different dimensions (0D, 1D, 2D, 3D) under thermal environments.

The thermal stability of phosphor materials had long been a bottleneck in their commercialization. Nowadays, cesium lead halide perovskite CsPbBr3 has been considered a potential replacement for the next generation of optoelectronic devices due to its excellent optical and electronic properties, however, the devices inevitably generate high temperatures on the surface under prolonged energization conditions in practical applications, which can be fatal to CsPbBr3. Despite the various strategies that have been employed to improve the thermal stability of CsPbBr3, systematic studies of the thermal stability of the basis CsPbBr3 are lacking. In this study, CsPbBr3 with different dimensions (0D quantum dots (QDs), 1D nanowires (NWs), 2D nanoplate (NPs), 3D micron crystals (MCs)) was prepared by traditional high-temperature thermal injection, and a systematic study was carried out on their optical properties and thermal stability. The results revealed that the dimensional change will directly influence the optical properties as well as the thermal stability of CsPbBr3. In particular, 3D CsPbBr3 MCs maintained relatively high thermal stability under high-temperature environments, which will bring interest for the commercialization of next-generation perovskite optoelectronic devices.

Preparation of CsPb(Cl/Br)3/TiO2:Eu3+ composites for white light emitting diodes.

The inherent single narrow emission peak and fast anion exchange process of cesium lead halide perovskite CsPbX3 (X = Cl, Br, I) nanocrystals severely limited its application in white light-emitting diodes. Previous studies have shown that composite structures can passivate surface defects of NCs and improve the stability of perovskite materials, but complex post-treatment processes commonly lead to dissolution of NCs. In this study, CsPb(Cl/Br)3 NCs was in-situ grown in TiO2 hollow shells doped with Eu3+ ions by a modified thermal injection method to prepare CsPb(Cl/Br)3/TiO2:Eu3+ composites with direct excitation of white light without additional treatment. Among them, the well-crystalline TiO2 shells acted as both a substrate for the dopant, avoiding the direct doping of Eu3+ into the interior of NCs to affect the crystal structure of the perovskite materials, and also as a protection layer to isolate the contact between PL quenching molecules and NCs, which significantly improves the stability. Further, the WLED prepared using the composites had bright white light emission, luminous efficiency of 87.39 lm/W, and long-time operating stability, which provided new options for the development of perovskite devices.

A Computationally Assisted Approach for Designing Wearable Biosensors toward Non-Invasive Personalized Molecular Analysis.

Wearable sweat sensors have the potential to revolutionize precision medicine as they can non-invasively collect molecular information closely associated with an individual's health status. However, the majority of clinically relevant biomarkers cannot be continuously detected in situ using existing wearable approaches. Molecularly imprinted polymers (MIPs) are a promising candidate to address this challenge but haven't yet gained widespread use due to their complex design and optimization process yielding variable selectivity. Here, QuantumDock is introduced, an automated computational framework for universal MIP development toward wearable applications. QuantumDock utilizes density functional theory to probe molecular interactions between monomers and the target/interferent molecules to optimize selectivity, a fundamentally limiting factor for MIP development toward wearable sensing. A molecular docking approach is employed to explore a wide range of known and unknown monomers, and to identify the optimal monomer/cross-linker choice for subsequent MIP fabrication. Using an essential amino acid phenylalanine as the exemplar, experimental validation of QuantumDock is performed successfully using solution-synthesized MIP nanoparticles coupled with ultraviolet-visible spectroscopy. Moreover, a QuantumDock-optimized graphene-based wearable device is designed that can perform autonomous sweat induction, sampling, and sensing. For the first time, wearable non-invasive phenylalanine monitoring is demonstrated in human subjects toward personalized healthcare applications.

Sr2+doped CsPbBrI2perovskite nanocrystals coated with ZrO2for applications as white LEDs.

Perovskite nanocrystals (NCs) feature adjustable bandgap, wide absorption range, and great color purity for robust perovskite optoelectronic applications. Nevertheless, the absence of lasting stability under continues energization, is still a major hurdle to the widespread use of NCs in commercial applications. In particular, the reactivity of red-emitting perovskites to environmental surroundings is more sensitive than that of their green counterparts. Here, we present a simple synthesis of ultrathin ZrO2coated, Sr2+doped CsPbBrI2NCs. Introducing divalent Sr2+may significantly eliminate Pb° surface traps, whereas ZrO2encapsulation greatly improves environmental stability. The photoluminescence quantum yield of the Sr2+-doped CsPbBrI2/ZrO2NCs was increased from 50.2% to 87.2% as a direct consequence of the efficient elimination of Pb° surface defects. Moreover, the thickness of the ZrO2thin coating gives remarkable heat resistance and improved water stability. Combining CsPbSr0.3BrI2/ZrO2NCs in a white light emitting diode (LED) with an excellent optical efficiency (100.08 lm W-1), high and a broad gamut 141% (NTSC) standard. This work offers a potential method to suppress Pb° traps by doping with Sr2+and improves the performance of perovskite NCs by ultrathin coating structured ZrO2, consequently enabling their applicability in commercial optical displays.

In Situ Fabrication of Lead-Free Double Perovskite/Polymer Composite Films for Optoelectronic Devices and Anticounterfeit Printing.

Lead-free double perovskites (DP) have the potential to become a rising star in the next generation of lighting markets by addressing the toxicity and instability issues associated with traditional lead-based perovskites. However, high concentrations of hydrochloric acid (HCl) were often employed as a solvent in the preparation of most DPs, accompanied by slow crystallization at high temperatures, which not only raised the risk and cost in the preparation process, but also had a potential threat to the environment. Here, an in situ fabrication strategy was proposed to realize the crystallization of DP in the polymer at low temperature with a mild dimethyl sulfoxide (DMSO) solvent, and subsequently obtained optically well-behaved Cs2Na0.8Ag0.2BiCl6/PMMA composite films (CFs) by doping with Ag+, generating bright orange luminescence with a photoluminescence quantum yield (PLQY) of up to 21.52%. Moreover, the growth dynamics of Cs2Na0.8Ag0.2BiCl6/PMMA CFs was further investigated by in situ optical transformation, which was extended to other DP-based polymer CFs. Finally, these CFs exhibited excellent performance in optoelectronic devices and anticounterfeit printing, the results of which provide a new pathway to advance the development of lead-free DP materials in the optical field.

Preparation of ultra-stable and environmentally friendly CsPbBr3@ZrO2/PS composite films for white light-emitting diodes.

The working stability of perovskite light-emitting diodes (LEDs) has become an urgent bottleneck to be solved in the process of commercialization. Although lead halide perovskite CsPbX3 (X = Br, I, Cl) quantum dots (QDs) are considered rising stars in the lighting market owing to their excellent optoelectronic properties, they suffer from fluorescence quenching under thermal conditions. Unfortunately, the surfaces of electronic devices inevitably warm up under long-term energization, which is extremely detrimental to the appropriate functioning of CsPbX3 QDs. Based on the above discussion, the relationship function between the energization time and surface temperature of electronic devices was analyzed, after which a strategy for the preparation of dual-encapsulating perovskites using organic (polystyrene (PS)) and inorganic (ZrO2) materials was proposed, and the change in optical stability before and after encapsulation was investigated. The results show that the thermal stability of CsPbBr3@ZrO2/PS composite films (CFs) after the dual encapsulation was remarkably enhanced, and the assembled white LEDs still retain the initial emission intensity under prolonged high-power operation. In addition, the double encapsulation layer completely suppresses the ion leakage in CsPbBr3 and avoids damage to the ecosystem. It can be seen that this encapsulation strategy was capable of imparting excellent working stability to the perovskite material, which would clear the obstacles to commercial conversion.

A wearable electrochemical biosensor for the monitoring of metabolites and nutrients.

Wearable non-invasive biosensors for the continuous monitoring of metabolites in sweat can detect a few analytes at sufficiently high concentrations, typically during vigorous exercise so as to generate sufficient quantity of the biofluid. Here we report the design and performance of a wearable electrochemical biosensor for the continuous analysis, in sweat during physical exercise and at rest, of trace levels of multiple metabolites and nutrients, including all essential amino acids and vitamins. The biosensor consists of graphene electrodes that can be repeatedly regenerated in situ, functionalized with metabolite-specific antibody-like molecularly imprinted polymers and redox-active reporter nanoparticles, and integrated with modules for iontophoresis-based sweat induction, microfluidic sweat sampling, signal processing and calibration, and wireless communication. In volunteers, the biosensor enabled the real-time monitoring of the intake of amino acids and their levels during physical exercise, as well as the assessment of the risk of metabolic syndrome (by correlating amino acid levels in serum and sweat). The monitoring of metabolites for the early identification of abnormal health conditions could facilitate applications in precision nutrition.

Cu3(PO4)2/BiVO4 photoelectrochemical sensor for sensitive and selective determination of synthetic antioxidant propyl gallate.

Propyl gallate (PG) as one of the most important additives has been widely used to prevent or slow the oxidation of foods in the food industry. In this work, Cu3(PO4)2/BiVO4 composite is synthesized through two hydrothermal processes. With visible light irradiation, the Cu3(PO4)2/BiVO4 composites modified PEC platform displays a superior anode photocurrent signal. The PEC sensor showed a wide linear range from 1 × 10-10 to 1 × 10-3 mol L-1 with a detection limit as low as 0.05 × 10-10 mol L-1. The Cu3(PO4)2/BiVO4 photoelectrochemical (PEC) sensor is designed and characterized by electrochemical impedance. Compared with GCE/BiVO4 and GCE/Cu3(PO4)2, the GCE/Cu3(PO4)2/BiVO4 has a higher photocurrent response. In addition, the sensor is highly selective for samples containing other antioxidants. Furthermore, the sensor can be used to detect PG in edible oil samples with satisfactory results. The recoveries of propyl gallate in edible oil ranged from 95.5 to 101.8%. The results show that Cu3(PO4)2/BiVO4 composites can be used to analyze PG in different edible oil samples, which are beneficial for food quality monitoring and reduce the risk of PG overuse in food.

Electrochemically driven optical and SERS immunosensor for the detection of a therapeutic cardiac drug.

Cardiovascular diseases pose a serious health risk and have a high mortality rate of 31% worldwide. Digoxin is the most commonly prescribed pharmaceutical preparation to cardiovascular patients particularly in developing countries. The effectiveness of the drug critically depends on its presence in the therapeutic range (0.8-2.0 ng mL-1) in the patient's serum. We fabricated immunoassay chips based on QD photoluminescence (QDs-ELISA) and AuNP Surface Enhanced Raman Scattering (SERS-ELISA) phenomena to detect digoxin in the therapeutic range. Digoxin levels were monitored using digoxin antibodies conjugated to QDs and AuNPs employing the sandwich immunoassay format in both the chips. The limit of detection (LOD) achieved through QDs-ELISA and SERS-ELISA was 0.5 ng mL-1 and 0.4 ng mL-1, respectively. It is demonstrated that the sensitivity of QDs-ELISA was dependent on the charge transfer mechanism from the QDs to the antibody through ionic media, which was further explored using electrochemical impedance spectroscopy. We demonstrate that QDs-ELISA was relatively easy to fabricate compared to SERS-ELISA. The current study envisages replacement of conventional methodologies with small immunoassay chips using QDs and/or SERS-based tags with fast turnaround detection time as compared to conventional ELISA.

Tuning optical properties of CsPbBr3by mixing Nd3+trivalent lanthanide halide cations for blue light emitting devices.

In recent years, significant progress has been made in the red and green perovskite quantum dots (PQDs) based light-emitting devices. However, a scarcity of blue-emitting devices that are extremely efficient precludes their research and development for optoelectronic applications. Taking advantage of tunable bandgaps of PQDs over the entire visible spectrum, herein we tune optical properties of CSPbBr3by mixing Nd3+trivalent lanthanide halide cations for blue light-emitting devices. The CsPbBr3PQDs doped with Nd3+trivalent lanthanide halide cations emitted strong photoemission from green into the blue region. By adjusting their doping concentration, a tunable wavelength from (515 nm) to (450 nm) was achieved with FWHM from (37.83 nm) to (16.6 nm). We simultaneously observed PL linewidth broadening thermal quenching of PL and the blue shift of the optical bandgap from temperature-dependent PL studies. The Nd3+cations into CsPbBr3PQDs more efficiently reduced non-radiative recombination. As a result of the efficient removal of defects from PQDs, the photoluminescence quantum yield (PLQY) has been significantly increased to 91% in the blue-emitting region. Significantly, Nd3+PQDs exhibit excellent long-term stability against the external environment, including water, temperature, and ultraviolet light irradiation. Moreover, we successfully transformed Nd3+doped PQDs into highly fluorescent nanocomposites. Incorporating these findings, we fabricate and test a stable blue light-emitting LED with EL emission at (462 nm), (475 nm), and successfully produce white light emission from Nd3+doped nanocomposites with a CIE at (0.32, 0.34), respectively. The findings imply that low-cost Nd3+doped perovskites may be attractive as light converters in LCDs with a broad color gamut.

CdS/Ti3C2 heterostructure-based photoelectrochemical platform for sensitive and selective detection of trace amount of Cu2.

Photoelectrochemical (PEC) detection as a potential development strategy for Cu2+ ion sensor has arisen extensive attention. Herein, CdS/Ti3C2 heterostructure was synthesized by electrostatically driven assembly and hydrothermal method. On the basis of a CdS/Ti3C2 heterostructure, a novel anodic PEC sensing platform was constructed for highly sensitive detection of trace amount of Cu2+. Carrier transport at the interface of CdS/Ti3C2 heterostructure was tremendously improved, due to the generation of effective Schottky junctions. Under visible light irradiation, the CdS/Ti3C2 heterostructure-modified PEC platform exhibits great anode photocurrent signal, and the formation of CuxS reduces the PEC response with the presence of Cu2+ as a representative analyte. Thus, the linear response of Cu2+ ranges from 0.1 nM to 10 µM and the limits of detection (LOD, 0.05 nM) are obtained, which is lower than that of WHO's Guidelines for Drinking-water Quality (30 µM). This idea of component reconstitution provides a new paradigm for the design of advanced PEC sensors.

Strong violet emission from ultra-stable strontium-doped CsPbCl3 superlattices.

Among the lead halide perovskites, the photoluminescence quantum yields (PLQYs) of perovskite quantum dots (PQDs) in the violet region are the very lowest. This is an obstacle to the optical applications across the entire visible area based on perovskite materials. Herein, we report a novel strontium (Sr)-substitution along with chlorine passivation strategy to enhance the PLQYs of CsPbCl3 PQDs. We surprisingly found that when the molar ratio of Sr2+/Pb2+ = 0.1/0.9, CsSr0.1Pb0.9Cl3 PQDs exhibit strong single-color violet emission, which is attributed to the effective passivation of chlorine defects. We further found spontaneous self-assembly of PQDs into highly emissive PSCs from the precursor in a highly concentrated solution. Moreover, by dilution of these PSCs, a few small PQD aggregates can be regained, which is similar to the PQDs formed at lower concentrations. Benefiting from the superior collective properties of individual PQDs, these highly fluorescent CsSr0.1Pb0.9Cl3 PSCs can maintain good stability even when directly immersed in water or exposed to illumination.

Ultrasensitive photoelectrochemical platform with micro-emulsion-based p-type hollow silver iodide enabled by low solubility product (Ksp) for H2S sensing.

Since visible-light (VL) accounting for massive solar radiation energy, a large amount of attention has been paid to the development of highly efficient visible-light-driven (VLD) semiconductor materials. However, despite recent efforts to construct VL active material, hollow structure-based silver iodide (AgI) with appropriate band gap and a large surface area are limited because of lack of a proper synthesis method. Herein, hollow AgI with p-type semiconductor behavior is constructed on the basis of micro-emulsion strategy, which enables admirable cathode photoelectrochemical (PEC) response. The as-prepared hollow AgI is applied to fabricate the PEC sensing platform and reveals a low limit of detection of 0.04 fM and a wide dynamic range up to 5 orders of magnitude toward H2S. The PEC sensing mechanism is supposed to the 'signal-off' pattern on account of the ultralow solubility product (Ksp) of Ag2S, derived from the precipitation reaction due to the high affinity between sulfide ion and Ag+. Besides, the hollow structure of AgI provides sufficient surface area forin situproducing Ag2S that serves as recombination center of carrier, thus causing the efficient quenching of photocurrent signals. This work broadens the horizon of structuring VLD semiconductor nanomaterials andKsp-based H2S sensing.