Bulk/Surface Defects Engineered TiO2 Nanotube Photonic Crystals Coupled with Plasmonic Gold Nanoparticles for Effective in Vivo Near-Infrared Light Photoelectrochemical Detection

Red and near-infrared light-activated photoelectrochemical nanobiosensors for biomedical target detection

Photoelectrochemical (PEC) nanobiosensors integrate molecular (bio)recognition elements with semiconductor/plasmonic photoactive nanomaterials to produce measurable signals after light-induced reactions. Recent advancements in PEC nanobiosensors, using light-matter interactions, have significantly improved sensitivity, specificity, and signal-to-noise ratio in detecting (bio)analytes. Tunable nanomaterials activated by a wide spectral radiation window coupled to electrochemical transduction platforms have further improved detection by stabilizing and amplifying electrical signals. This work reviews PEC biosensors based on nanomaterials like metal oxides, carbon nitrides, quantum dots, and transition metal chalcogenides (TMCs), showing their superior optoelectronic properties and analytical performance for the detection of clinically relevant biomarkers. Furthermore, it highlights the innovative role of red light and NIR-activated PEC nanobiosensors in enhancing charge transfer processes, protecting them from biomolecule photodamage in vitro and in vivo applications. Overall, advances in PEC detection systems have the potential to revolutionize rapid and accurate measurements in clinical diagnostic applications. Their integration into miniaturized devices also supports the development of portable, easy-to-use diagnostic tools, facilitating point-of-care (POC) testing solutions and real-time monitoring.

Highly ordered nanocavity as photonic-plasmonic-polaritonic resonator for single molecule miRNA SERS detection

Strong light-matter coupling between molecules and electromagnetic field lead to the formation of hybrid polaritonic states for surface enhanced Raman scattering (SERS) detection. However, owing to the inefficient interaction between zero-point fluctuations of photons/plasmons and molecular electronic transitions, the Raman enhancement is limited in relative low levels. Here, we propose and fabricate a TiOx/Cu2-xSe/R6G nanocavity based photonic-plasmonic-polaritonic resonator for single molecular SERS detection. Through precisely matching the energy levels of illuminated photon, generated plasmon, and molecular polariton, an extremely high Raman enhancement factor of 2.6 × 109 is implemented. The rationally designed SERS substrate allows sensitive detection of miRNA-21 in single molecular level with a detection limit of 1.58 aM. The hybrid SERS mechanism both from electromagnetic and chemical perspectives in this photonic-plasmonic-polaritonic resonance strategy provides insight into polaritonic semiconductor systems, thus paving the way for new experimental possibilities in light-matter hybrids.

High-Throughput Multitarget Molecular Detection in an Automatic Light-Addressable Photoelectrochemical Sensing Platform

Successively emerged high-throughput multitarget molecular detection methods bring significant development tides in chemical, biological, and environmental fields. However, several persistent challenges of intricate sample preparation, expensive instruments, and tedious and skilled operations still need to be further addressed. Here, we propose an automatic light-addressable photoelectrochemical (ALA-PEC) sensing platform for sensitive and selective detection of multitarget molecules. With Au nanoparticle-decorated TiO2 nanotube photonic crystals (Au-TiO2 NTPCs) as a photoelectrode and 8 kinds of antibiotics as target molecules, the ALA-PEC sensing system implements automatic detection of multimolecules in a short time with high sensitivity and good selectivity. Random samples with different amounts of antibiotics have been well-distinguished in the ALA-PEC system, and both the chemical components and concentrations have been well-illustrated in a pattern recognition model. It is worth noting that 8 samples are not the limit of the ALA-PEC sensing platform, which can be easily expanded to more complex detection arrays based on practical needs. The emerging ALA-PEC sensing platform provides a new solution for rapid screening and detection of multitarget and high-throughput substances and potentially brings the automatic, portable, sensitive, high-throughput, and cost-effective detection technique to an entire new realm.

Photonic-plasmonic resonator for SERS biodetection

To improve the laser utilization efficiency and avoid photodamage in surface-enhanced Raman spectroscopy (SERS), it is imperative to introduce photon technology into the field of SERS detection. A major challenge is the inefficient interaction between the substrate and the incident wavelength, resulting in limited Raman enhancement at a relatively low level. Here, we sputtered plasmonic Au nanoparticles (NPs) onto photonic TiOx nanocavities, creating a novel hybrid photonic-plasmonic resonator that achieves a large degree of optical manipulation and long-term localization. By facilely controlling the size of Au NPs, the resonance wavelength of plasmonic Au NPs can be matched with the photonic nanocavity to maximize the light trapping intensity, which leads to a synergistic enhancement of SERS via the electromagnetic and chemical mechanisms, resulting in a SERS enhancement up to 1.75 × 109 under non-resonant excitation. In particular, the substrate can achieve strong absorption and localization for long wavelengths, thus enabling a large SERS enhancement with a small light intensity, which can effectively avoid the photodamage that may occur in Raman testing. The substrate can detect various biomolecules, including biomarkers in serum, thus realizing the differentiation of different cancers. This study provides a powerful and sensitive platform for SERS, facilitating bioanalysis and disease diagnosis in complex systems.

Upconversion-Powered Photoelectrochemical Bioanalysis for DNA Sensing

In this work, we report a new concept of upconversion-powered photoelectrochemical (PEC) bioanalysis. The proof-of-concept involves a PEC bionanosystem comprising a NaYF4:Yb,Tm@NaYF4 upconversion nanoparticles (UCNPs) reporter, which is confined by DNA hybridization on a CdS quantum dots (QDs)/indium tin oxide (ITO) photoelectrode. The CdS QD-modified ITO electrode was powered by upconversion absorption together with energy transfer effect through UCNPs for a stable photocurrent generation. By measuring the photocurrent change, the target DNA could be detected in a specific and sensitive way with a wide linear range from 10 pM to 1 μM and a low detection limit of 0.1 pM. This work exploited the use of UCNPs as signal reporters and realized upconversion-powered PEC bioanalysis. Given the diversity of UCNPs, we believe it will offer a new perspective for the development of advanced upconversion-powered PEC bioanalysis.

Recent Progress in Photoelectrochemical Sensing of Pesticides in Food and Environmental Samples: Photoactive Materials and Signaling Mechanisms

Pesticides have become an integral part of modern agricultural practices, but their widespread use poses a significant threat to human health. As such, there is a pressing need to develop effective methods for detecting pesticides in food and environmental samples. Traditional chromatography methods and common rapid detection methods cannot satisfy accuracy, portability, long storage time, and solution stability at the same time. In recent years, photoelectrochemical (PEC) sensing technology has gained attention as a promising approach for detecting various pesticides due to its salient advantages, including high sensitivity, low cost, simple operation, fast response, and easy miniaturization, thus becoming a competitive candidate for real-time and on-site monitoring of pesticide levels. This review provides an overview of the recent advancements in PEC methods for pesticide detection and their applications in ensuring food and environmental safety, with a focus on the categories of photoactive materials, from single semiconductor to semiconductor-semiconductor heterojunction, and signaling mechanisms of PEC sensing platforms, including oxidation of pesticides, steric hindrance, generation/decrease in sacrificial agents, and introduction/release of photoactive materials. Additionally, this review will offer insights into future prospects and confrontations, thereby contributing novel perspectives to this evolving domain.

Fabrication of near infrared light responsive photoelectrochemical immunosensor for in vivo detection of melanoma cells

Effective and convenient detection of melanoma cells with high sensitivity is essential to identify malignant melanoma in its early stage. However, the existing detection methods, such as immunohistochemical analysis, are too complicated and time-consuming to realize the convenient in vivo and in situ detection. Herein, a near infrared responsive photoelectrochemical (PEC) immunosensor is proposed with plasmonic Au nanoparticles-photonic TiO2 nanocaves (Au/TiO2 NCs) as photon harvest and conversion transducer and antibody as cell recognition unit. The micro-antibody/Au/TiO2 NCs photoelectrode can easily in vivo distinguish melanoma cells and can realize sensitive detection of melanoma cells in short time of 1 min with a lowest limit of detection of 2 cell mL-1. The PEC immunosensor strategy not only allows us to pioneeringly implement sensitive in vivo bio-detection, but also opens up a new avenue for rational design of cell recognition units and micro-electrode for universal and reliable bio-detections.

Bone-mimicking scaffold based on silk fibroin incorporated with hydroxyapatite and titanium oxide as enhanced osteo-conductive material for bone tissue formation: fabrication, characterization, properties, andin vitrotesting

Bone-mimicking scaffolds based on silk fibroin (SF) mixed with hydroxyapatite nanoparticles (HA NPs) and titanium oxide (TiO2) nanoparticles were created as materials for bone formation. Six scaffold groups were fabricated: S1 (SF), S2 (Silk + (HA: TiO2; 100: 0)), S3 (Silk, (HA: TiO2; 70: 30)), S4 (Silk + (HA NPs: TiO2; 50: 50)), S5 (Silk + (HA: TiO2; 30: 70)), and S6 (Silk + (HA NPs: TiO2; 0:100)). Scaffolds were characterized for molecular formation, structure, and morphology by Fourier transform infrared spectroscopy, element analysis, and X-ray diffraction. They were tested for physical swelling and compressive modulus. Scaffolds were cultured with MC3T3 and testedin vitroto evaluate their biological performance. The results showed that scaffolds with HA and TiO2demonstrated molecular interaction via amide I and phosphate groups. These scaffolds had smaller pore sizes than those without HA and TiO2. They showed more swelling and higher compressive modulus than the scaffolds without HA and TiO2. They exhibited better biological performance: cell adhesion, viability, proliferation, alkaline phosphatase activity, and calcium content than the scaffolds without HA and TiO2. Their porous walls acted as templates for cell aggregation and supported synthesis of calcium secreted from cells. S3 were the most suitable scaffolds. With their enhanced osteo-conductive function, they are promising for bone augmentation for oral and maxillofacial surgery.

Interfacial States in Au/Reduced TiO2 Plasmonic Photocatalysts Quench Hot-Carrier Photoactivity

Understanding the interface of plasmonic nanostructures is essential for improving the performance of photocatalysts. Surface defects in semiconductors modify the dynamics of charge carriers, which are not well understood yet. Here, we take advantage of scanning photoelectrochemical microscopy (SPECM) as a fast and effective tool for detecting the impact of surface defects on the photoactivity of plasmonic hybrid nanostructures. We evidenced a significant photoactivity activation of TiO2 ultrathin films under visible light upon mild reduction treatment. Through Au nanoparticle (NP) arrays deposited on different reduced TiO2 films, the plasmonic photoactivity mapping revealed the effect of interfacial defects on hot charge carriers, which quenched the plasmonic activity by (i) increasing the recombination rate between hot charge carriers and (ii) leaking electrons (injected and generated in TiO2) into the Au NPs. Our results show that the catalyst's photoactivity depends on the concentration of surface defects and the population distribution of Au NPs. The present study unlocks the fast and simple detection of the surface engineering effect on the photocatalytic activity of plasmonic semiconductor systems.

A near-infrared photoelectrochemical aptasensing system based on Bi2O2S nanoflowers and gold nanoparticles for high-performance determination of MCF-7 cells

Circulating tumor cells (CTCs) are commonly considered as the major cause of tumor metastasis and can eventually lead to death. Therefore, developing a high-performance method for the determination of CTCs is very significant for promoting the cancer survival rate. Photoelectrochemical biosensing systems have been extensively investigated and applied for bioassays. Herein, Bi₂O₂S nanoflowers were successfully prepared through a simple one-step hydrothermal method. After being integrated with gold nanoparticles with a diameter of ∼45 nm, AuNPs/Bi₂O₂S nanocomposites were coated onto an ITO electrode surface to build a photoelectrochemical sensing platform which can be excited with near-infrared light to produce photocurrent response. Subsequently, mercapto-group functionalized aptamer (SH-Apt) was fixed onto the AuNPs/Bi₂O₂S/ITO surface. Due to the overexpress of MUC1 protein in the cell membrane, MCF-7 cells were specifically trapped on the SH-Apt/AuNPs/Bi₂O₂S/ITO surface. The introduce of MCF-7 cells lead to an obvious decrease on the photocurrent response. The photocurrent variation shows a satisfied linear relationship to the logarithm of MCF-7 cells concentration ranged from 50 to 6 × 10⁵ cell mL^-1. The detection limit obtained is 17 cell mL^-1. The PEC biosensor shows excellent sensitivity, selectivity and stability for sensing MCF-7 cells, even for determining MCF-7 cells in clinical serum samples.

A near-infrared photoelectrochemical immunosensor for CA72-4 sensing based on SnS nanorods integrated with gold nanoparticles

SnS nanorods with near-infrared photoelectric conversion characteristics were successfully synthesized through a simple hydrothermal method. Gold nanoparticles were self-assembled onto SnS nanorods surface to form SnS/AuNPs nanocomposites. The integration of AuNP can significantly improve the photocurrent response of SnS nanorods under being illuminated with 808 nm near-infrared light. A near-infrared photoelectrochemical immunosensing platform based on SNS/AuNPs nanocomposites was constructed for sensing gastric cancer tumor marker CA72-4. Experimental conditions were optimized to improve the immunosensing performances for CA72-4 determination. As CA72-4 concentration varied from 0.01 to 50 U mL^-1, the photocurrent variation between the immunosensor before and after reacting with CA72-4 was linearly related to the logarithm of its concentration. The detection limit was calculated to be 0.008 U mL^-1. The practicability of the immunosensor was demonstrated by determining CA72-4 in human serum samples.

Signal-On Near-Infrared Photoelectrochemical Aptasensors for Sensing VEGF165 Based on Ionic Liquid-Functionalized Nd-MOF Nanorods and In-Site Formation of Gold Nanoparticles

The low photon energy and deep penetrating ability of near-infrared (NIR) light make it an ideal light source for a photoelectrochemical (PEC) immunosensing system. Absorption wavelengths of the metal-organic frameworks (MOFs) can be regulated by adjusting the metal ions and the conjugation degree of the ligands. Herein, an ionic liquid with a large conjugated structure was synthesized and was used as a ligand to coordinate with Nd ions to prepare Nd-MOF nanorods with a band gap of 1.26 eV. The Nd-MOF rods show a good photoabsorption property from 200 to 980 nm. A PEC platform was constructed by using Nd-MOF nanorods as the photoelectroactive element. A detachable double-stranded DNA labeled with alkaline phosphatase (ALP), which is specific to VEGF165, was immobilized onto the PEC sensing interface. After blocking unspecific active sites with bovine albumin, an NIR PEC aptasensing system was developed for VEGF165 detection. After being incubated in a mixture of VEGF165, l-ascorbic acid 2-phosphate (magnesium salt hydrate) (AAP), and chloroauric acid, the aptamers for VEGF165 were detached from the PEC aptasensing interface, thus resulting in the decrease of the charge-transfer resistance and the increase of the photocurrent response. The shedding of the aptamers also makes the ALP approach the electrode surface, thus catalyzing the reduction of AAP to produce ascorbic acid (AA). Subsequently, AA reduces in situ chloroauric acid to produce AuNPs on the Nd-MOF-based sensing interface. With the excellent conductivity and localized surface plasmon resonance effect, the AuNPs can accelerate the separation of electron-hole pairs generated from Nd-MOF nanorods, thus promoting the photoelectric conversion efficiency and achieving signal amplification. Under optimized conditions, the PEC responses were linearly related to the VEGF165 concentrations in the range of 0.01-100 ng mL^-1 and exhibit a low detection limit of 3.51 pg mL^-1 (S/N = 3). VEGF165 in human serum samples was detected by the NIR PEC aptasensor. Their concentrations were found to be well consistent with that obtained from ELISA. Furthermore, the PEC aptasensor demonstrated recoveries from 96.07 to 103.8%. The relative standard deviations were within 5%, indicating good accuracy and precision. The results further verify its practicability for clinical diagnosis.

Zwitterionic Polymers Coating Antibiofouling Photoelectrochemical Aptasensor for In Vivo Antibiotic Metabolism Monitoring and Tracking

Long-term in vivo monitoring and tracking of target molecules in living organism is essential to reveal vital physiological activity. However, undesirable contamination of protein and biological cells may bring serious biofouling issues. Herein, zwitterionic sulfobetaine methacrylate (SBMA) polymers are grafted on the TiO₂ nanotube (NT) surface with polydopamine (PDA) as linker to fabricate a TiO₂ NTs/PDA/SBMA photoelectrode. The TiO₂ NTs/PDA/SBMA/aptamer-based PEC aptasensor can be sensitive and have selective detection of target molecules with excellent antibiofouling activity. Beneficial from the above advantages, the implantable micro-PEC aptasensor has implemented in vivo tracking and monitoring of the metabolism of antibiotics in a living mouse. The robust antibiofouling property generates new inquiries and an approach for long-standing questions in a new way for reliable and long-term sensing of vital biomolecules in complex biological fluids and uncovers a promising advance of intrinsic physiological mechanisms.

A visible and near-infrared light dual responsive "signal-off" and "signal-on" photoelectrochemical aptasensor for prostate-specific antigen

A visible and near-infrared light dual responsive "signal-off" and "signal-on" photoelectrochemical aptasensor was constructed for determining prostate-specific antigen (PSA) based on MoS₂ nanoflowers and gold nanobipyramids. The dual responsive photoelectrochemical aptasensor can provide accurate results for PSA determination. For the photoelectrochemical aptasensor fabrication, amino-group functionalized aptamers were immobilized on a MoS₂ nanoflowers modified glassy carbon electrode surface for the specific recognition, and thus to achieve a "signal-off" aptasensor for PSA under visible light illumination. Subsequently, gold nanobipyramids integrated with thiol-functional aptamer were introduced to the "signal-off" aptasensing interface after PSA recognition. Under excitation with near-infrared light at 808 nm, the photocurrent response can be amplified significantly due to the excellent conductivity and local surface plasmon resonance effect of gold nanobipyramids, thus to producing a "signal-on" model for determining PSA. Under the optimized conditions, the dual-responsive photoelectrochemical aptasensor shows a linear response to the logarithm of PSA concentration in the range of 0.005-100 ng/mL. The detection limits for PSA determination with a "signal-off" or a "signal-on" mode are 1.75 pg mL^-1 and 0.39 pg mL^-1, respectively. The dual-responsive photoelectrochemical aptasensor was also employed for determining PSA in clinical serum samples with satisfactory selectivity and excellent accuracy.

Visible light-driven self-powered aptasensors for ultrasensitive Microcystin-LR detection based on the carrier density effect of N-doped graphene hydrogel/hematite Schottky junctions

In this work, a novel visible light-driven self-powered photoelectrochemical (PEC) platform was designed based on 3D N-doped graphene hydrogel/hematite nanocomposites (NGH/Fe₂O₃) via a facile one-pot hydrothermal route. The coupling NGH with Fe₂O₃ could generate a Schottky junction, which promoted the separation of charges. Moreover, Mott-Schottky measurements validated that the carrier concentration achieved by NGH/Fe₂O₃ was about 3.4 × 10³ times in comparison to that of pure Fe₂O₃, which was beneficial for efficient charge transfer. Owing to the carrier density effect and Schottky junction, the photocurrent of the as-fabricated NGH/Fe₂O₃ nanocomposites was 6.9-fold higher than that of pure Fe₂O₃. On the basis of such excellent Schottky junctions, an ultrasensitive visible light-induced self-powered PEC aptasensor was developed using a Microcystin-LR (MC-LR) aptamer. The as-fabricated PEC aptasensor displayed good analytical performance toward MC-LR detection in terms of wide linear range (1 pM-5 nM), low detection limit (0.23 pM, S/N = 3), excellent selectivity and high stability. This new strategy can provide a way for regulating nanostructures for more sensitive PEC sensors by increasing the carrier density.

Unprecedented Improvement of Near-Infrared Photothermal Conversion Efficiency to 87.2% by Ultrafast Non-radiative Decay of Excited States of Self-Assembly Cocrystal

Near-infrared (NIR) photothermal conversion is of great interest in many fields. Here, a self-assembly organic cocrystal (N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) and pyromellitic dianhydride (PMDA)) with strong absorption in NIR range is constructed, with widespread absorption (200-1500 nm) and very high NIR photothermal conversion efficiency (87.2%). Essentially, in this cocrystal, a small HOMO-LUMO gap of donor-acceptor pair boosts the absorption ability of this cocrystal in the NIR range. The mixed stacking structure significantly enhances the intermolecular interactions as well as the electron-hole delocalization, suppressing the emission processes, leading to nonradiative decay processes from excited states. Strong intermolecular interactions enable the cocrystal to have dense electronic energy levels, leading to a high proportion (94.4%) vibrational cooling and internal conversion processes with ultrafast excited-state relaxation (0.12 ps), which contributes to high NIR photothermal conversion efficiency. Furthermore, the cocrystal has exhibited capable ability for being an excellent candidate for a NIR photothermal therapy agent.

Near-infrared photoactive Yb-MOF functionalized with a large conjugate ionic liquid: synthesis and application for photoelectrochemical immunosensing of carcinoma embryonic antigen

A novel near-infrared (NIR)-excited photoelectrochemical (PEC) immunosensor based on an ionic liquid functionalized metal organic framework (Yb-MOF) and gold nanoparticles (Au-NPs) was designed for the high-performance determination of carcinoembryonic antigen (CEA). The Yb-MOF was synthesized from the coordination of the Yb3+ metal ion with the 1,1'-(1,5-dihydropyrene-2,7-diyl)bis(3-(4-carboxybenzyl)-1H-imidazol-3-ium) bromide [DDPDBCBIm(Br)2] ionic liquid by a hydrothermal method. To improve the photoelectric conversion efficiency of the Yb-MOF in the NIR region, the surface of the Yb-MOF was integrated with gold nanoparticles (AuNPs) to fabricate a Yb-MOF@AuNP nanocomposite through an in situ reduction of chloroauric acid with sodium borohydride. The NIR photoelectrochemical response of the Yb-MOF@AuNPs at 808 nm was enhanced 4-fold over the pristine Yb-MOF. Subsequently, a photoelectrochemical platform based on the Yb-MOF@AuNPs was constructed for loading the CEA antibody (anti-CEA). After cross-linking with glutaraldehyde followed by blocking with bovine serum albumin, a photoelectrochemical sensor for assaying CEA was fabricated. Upon specifically interacting with CEA, CEA can block the photogenerated electron-hole pair transfer and the mass transfer of ascorbic acid to the sensing interface, thus leading to a decrease in photocurrent response. The photocurrent variation can be used for determining CEA quantitatively. After optimizing the experimental conditions, the photocurrent variations before and after incubation with CEA were linearly correlated with the CEA concentration over the range of 0.005-15 ng mL-1. The detection limit of CEA was calculated to be 0.25 pg mL-1 (S/N = 3). The immunosensor was employed for the measurement of free CEA in clinical serum samples, and the results were very consistent with the values obtained by clinical tests. The NIR PEC immunosensor also demonstrated excellent accuracy and recovery, which corroborates its potential as a practical technique in clinical diagnosis.

Competitive near-infrared PEC immunosorbent assay for monitoring okadaic acid based on a disposable flower-like WO3-Modified screen-printed electrode

The long-term toxic effects of okadaic acid (OA) in shellfish pose a serious threat to public health, negatively impacting the development of the shellfish aquaculture industry. In this study, a novel competitive near-infrared-mediated photoelectrochemical immunosorbent assay (cNIR-PECIA) was developed for ultrasensitive and highly selective detection of OA based on NaYF₄:Yb, Tm upconversion nanophosphors (UCNPs) and a flower-like WO₃-modified screen-printed electrode (FL-WO₃ SPE). The UCNPs function as a self-powder to convert NIR excitation into visible emissions. FL-WO₃ fully utilizes the visible illumination and induces the separation of electron-hole pairs, thus generating a photocurrent. After conjugating monoclonal antibodies against OA on UCNPs (UCNPs-Ab), the bright PEC immunoprobe selectively captured OA molecules, which were then determined by a competitive indirect immunosorbent assay. Under optimal conditions, the 50% inhibitory concentration of the immunosensor was 0.09 ng mL^-1. The OA concentration had a linear relationship with the antibody binding rate in the range of 0.01-60 ng mL^-1 with an extremely low detection limit of 0.007 ng mL^-1. Finally, the proposed cNIR-PECIA was successfully utilized to analyze OA content in mussel samples. This study affords new ideas for constructing NIR PEC sensors by using upconversion luminescent materials to match semiconductors. The superior sensing properties indicate their potential applicability in food safety analysis.

TiO2-sensitized double-shell ZnCdS hollow nanospheres for photoelectrochemical immunoassay of carcinoembryonic antigen coupled with hybridization chain reaction-dependent Cu2+ quenching

A novel photoelectrochemical immunosensor was constructed to monitor carcinoembryonic antigen (CEA) based on hybridization chain reaction (HCR)-mediated in situ generation of copper nanoparticles (Cu NPs) and subsequent Cu²⁺-dependent quenching reaction, in which titanium dioxide nanoparticles-sensitized double-shell zinc cadmium sulfide hollow nanospheres (TiO₂/DS-ZnCdS)-modified ITO electrode and anti-CEA antibody-modified 96-well plate served as biological recognition and signal detection platforms, respectively. The synergistic effect of TiO₂ NPs and DS-ZnCdS hollow nanospheres contributed to the improvement of photoelectric conversion efficiency, and HCR-mediated signal cascade benefited the enhancement of detection sensitivity. In the presence of CEA, biotin-labelled anti-CEA antibodies were immobilized onto anti-CEA antibody-modified 96-well plate, and triggered HCR process to form long double stranded DNA, which could adsorb a large number of Cu²⁺ ions and then in situ form Cu NPs on double stranded DNA template by a facile reduction reaction. After acid treatment, the dissolved Cu²⁺ ions could significantly reduce the photocurrent response due to the generation of Cu_xS. Under optimal conditions, the immunosensor exhibited a desirable liner range of 1 pg mL^-1 - 50 ng mL^-1 and a low detection limit of 0.1 pg mL^-1, as well as excellent selectivity and stability. Meanwhile, the recoveries of human serum sample analysis ranged from 96.8% to 103.6%, and the relative standard deviation was less than 7.40%, showing a good feasibility in early clinical diagnosis.

FRET Modulated Signaling: A Versatile Strategy to Construct Photoelectrochemical Microsensors for In Vivo Analysis

Microelectrode-based electrochemical (EC) and photoelectrochemical (PEC) sensors are promising candidates for in vivo analysis of biologically important chemicals. However, limited selectivity in complicated biological systems and poor adaptability to electrochemically non-active species restrained their applications. Herein, we propose the concept of modulating the PEC output by a fluorescence resonance energy transfer (FRET) process. The emission of energy donor was dependent on the concentration of target SO₂ , which in turn served as the modulator of the photocurrent signal of the photoactive material. The employment of optical modulation circumvented the problem of selectivity, and the as-fabricated PEC microelectrode showed good stability and reproducibility in vivo. It can monitor fluctuations of SO₂ levels in brains of rat models of cerebral ischemia-reperfusion and febrile seizure. More significantly, such a FRET modulated signaling strategy can be extended to diverse analytes.

Flame Synthesized Blue TiO2- x with Tunable Oxygen Vacancies from Surface to Grain Boundary to Bulk

Fabrication of nonstoichiometric metal oxides containing oxygen vacancies (OVs) has been an effective strategy to modulate their (photo)catalytic or (photo)electrochemical performances which are all affected by charge transfer at the interface and in the bulk. Considerable efforts are still needed to achieve tunability of OVs, as well as their quantitative characterization. Herein, a one-step flame synthesis method is reported for the first time for fast fabrication of blue TiO_{2- x} with controllable defect content and location. Temperature-programmed oxidation (TPO) analysis is applied for the first time and found to be an excellent technique in both differentiating and quantifying OVs at the surface, grain boundary (GB), and bulk of TiO_{2- x} . The results indicate that a moderate level of OVs can greatly enhance the charge transfer. Importantly, the OVs locked at GBs due to the thermal sintering of nanoparticles during the synthesis can facilitate the anchoring and reduction of Pt species.

Formation of a Photoelectrochemical Z-Scheme Structure with Inorganic/Organic Hybrid Materials for Evaluation of Receptor Protein Expression on the Membrane of Cancer Cells

Quantitative analysis of receptor protein expression is essential to give new insights into tumor-related research. Benefitting from their high sensitivity and low background, photoelectrochemical (PEC) platforms are considered as powerful tools for evaluating the expression of receptor proteins. Herein, to reduce the cytotoxicity and facilitate the subsequent assembly, l-cysteine-modified Ag-ZnIn₂S₄ quantum dots (l-Cys AZIS QDs) are prepared and PEC responses under the irradiation of long wavelength light are obtained. To further improve the PEC behavior, iron phthalocyanine (FePc) is employed to form a Z-scheme structure with l-Cys AZIS QDs. The Z-scheme structure based on l-Cys AZIS QDs/FePc hybrid materials exhibits high photo-to-electric conversion efficiency and can be excited with near-infrared range light. Because hyaluronic acid linked to photoactive materials can recognize CD44 expressed on the membrane of cancer cells, cancer cells are immobilized onto l-Cys AZIS QDs/FePc hybrid materials, inducing a decrease of the photocurrent intensity. Consequently, a PEC cytosensor is constructed to quantify cancer cells expressing CD44. The PEC analytical platform is able to determine A549 cells in the range of 2 × 10² to 4.5 × 10⁶ cells/mL, and a detection limit of 15 cells/mL is realized in the case of S/N = 3. In addition, the expression of CD44 in A549 and other five cancer cells is measured with this PEC method. Depending on our data, the expression of CD44 in different cancer cells is distinct, indicating great potential of this method in receptor protein-related studies.