Photoelectrochemical Cytosensing of RAW264.7 Macrophage Cells Based on a TiO2 Nanoneedls@MoO3 Array

Novel Ultrasensitive Photoelectrochemical Cytosensor Based on Hollow CdIn2S4/In2S3 Heterostructured Microspheres for HepG2 Cells Detection and Inhibitor Screening

Hepatocellular carcinoma is a life-threatening malignant tumor found around the world for its high morbidity and mortality. Therefore, it is of great importance for sensitive analysis of liver cancer cells (HepG2 cells) in clinical diagnosis and biomedical research. To fulfill this demand, hollow CdIn₂S₄/In₂S₃ heterostructured microspheres (termed CdIn₂S₄/In₂S₃ for clarity) were prepared by a two-step hydrothermal strategy and applied for building a novel photoelectrochemical (PEC) cytosensor for ultrasensitive and accurate detection of HepG2 cells through specific recognition of CD133 protein on the cell surface with the respective aptamer. The optical properties of CdIn₂S₄/In₂S₃ were investigated by UV-vis diffuse reflectance spectroscopy (DRS) and PEC technology. By virtue of their appealing PEC characteristics, the resultant PEC sensor exhibited a wider dynamic linear range from 1 × 10² to 2 × 10⁵ cells mL^-1 with a lower limit of detection (LOD, 23 cells mL^-1), combined by evaluating the expression level of CD133 protein stimulated by metformin as a benchmarked inhibitor. This work opens a valuable and feasible avenue for sensitive detection of diverse tumor cells, holding great potential in early clinical diagnosis and treatment coupled by screening inhibitors.

Surface Plasmon-Enhanced Photoelectrochemical Sensor Based on Au Modified TiO2 Nanotubes

Based on the enhanced charge separation efficiency of the one-dimensional structure and strong surface plasmon resonance (SPR) of gold, a gold modified TiO₂ nanotube (Au/TiO₂NTs) glucose photoelectrochemical (PEC) sensor was prepared. It could be activated by visible red light (625 nm). Under optimal conditions, the Au/TiO₂NTs sensor exhibited a good sensitivity of 170.37 μA·mM⁻¹·cm⁻² in the range of 1–90 μM (R² = 0.9993), and a detection limit of 1.3 μM (S/N = 3). Due to its high selectivity, good anti-interference ability, and long-term stability, the fabricated Au/TiO₂NTs sensor provides practical detection of glucose. It is expected to be used in the construction of non-invasive PEC biosensors.

Recent Advances of Nanostructured Materials for Photoelectrochemical Bioanalysis

Nowadays, the emerging photoelectrochemical (PEC) bioanalysis has drawn intensive interest due to its numerous merits. As one of its core elements, functional nanostructured materials play a crucial role during the construction of PEC biosensors, which can not only be employed as transducers but also act as signal probes. Although both chemical composition and morphology control of nanostructured materials contribute to the excellent analytical performance of PEC bioassay, surveys addressing nanostructures with different dimensionality have rarely been reported. In this review, according to classification based on dimensionality, zero-dimensional, one-dimensional, two-dimensional, and three-dimensional nanostructures used in PEC bioanalysis are evaluated, with an emphasis on the effect of morphology on the detection performances. Furthermore, using the illustration of recent works, related novel PEC biosensing patterns with promising applications are also discussed. Finally, the current challenges and some future perspectives in this field are addressed based on our opinions.

Introduction of an antifouling photoelectrode: an effective strategy for a high-performance photoelectrochemical cytosensor

As nonspecific adsorption or biofouling has obvious side effects on the selectivity, it is a great challenge for cytosensors to detect target cells in practical biological samples. In this study, we first propose the design and synthesis of an antifouling photoelectrode. The antifouling photoelectrode not only has the desired photocurrent response, but also possesses an unexpected antifouling capability of resisting nonspecific adsorption of biomolecules. Herein, the PEDOT-HPG/SnS/ZnO-NT antifouling photoelectrode was formed and a robust photoelectrochemical cytosensor with enhanced sensitivity and selectivity has been demonstrated.

Micro/Nano Electrode Array Sensors: Advances in Fabrication and Emerging Applications in Bioanalysis

Due to the rapid development of micro/nano manufacturing techniques and the greater understanding in electrochemical principles and methods, micro/nano electrode array sensing has received much attention in recent years, especially in bioanalysis. This review aims to explore recent progress in innovative techniques for the construction of micro/nano electrode array sensor and the unique applications of various types of micro/nano electrode array sensors in biochemical analysis. Moreover, the new area of smart sensing benefited from miniaturization of portable micro/nano electrode array sensors as well as wearable intelligent devices are further discussed.

Recognition of M2 type tumor-associated macrophages with ultrasensitive and biocompatible photoelectrochemical cytosensor based on Ce doped SnO2/SnS2 nano heterostructure

Tumor-associated macrophages (TAMs) play central roles in the regulation of tumor growth. TAMs can be differentiated into M1 and M2 types, which are responsible for the inhibition and growth of tumor tissues, respectively. Recognition of M2-TAMs is significant for the diagnosis and therapy of cancer, which is however severely limited due to the deficiency of selective and sensitive photoelectrochemical sensors. In this work, using Ce doped SnO₂/SnS₂ nano heterostructure as the highly sensitive platform, a photoelectrochemical sensor enabling the recognition of M2-TAMs was fabricated for the first time. By the decoration of CD163 antibody on the platform, the ultrasensitive photoelectrochemical sensor can selectively detect the CD163 protein on the surface of M2-TAMs. To our best knowledge, this is the first demonstration for recognition of M2-TAMs using photoelectrochemical method. The fabricated cytosensor has ultra-sensitive photocurrent response, applicable biological compatibility, high selectivity and relatively wide linear sensing range (5 × 10¹ to 1 × 10⁵ cells/ml) with a low detection limit (50 cells/ml) for the detection of M2-TAMS. This kind of PEC cytosensor would provide a novel analysis and detection strategy for M2-TAMs.

Dissociable photoelectrode materials boost ultrasensitive photoelectrochemical detection of organophosphorus pesticides

Generally, the photoactive materials are always tightly fixed on the photoelectrode of photoelectrochemical (PEC) sensors to produce excellent photocurrent response, while obvious and constant background currents will appear as well and then hamper the ultrasensitive sensing of target molecules. In this work, ultrasensitive detection of organophosphorus pesticides (OPs) is successfully fulfilled by using dissociable photoelectrode based on CdS nanocrystal-functionalized MnO₂ nanosheets. With the assistance of acetylcholinesterase (AChE), acetylthiocholine (ATCh) is hydrolyzed into thiocholine (TCh) which can effectively etch the ultrathin MnO₂ nanosheets, resulting in the dissociation of MnO₂-CdS from the photoelectrode. Benefiting from the dissociation of photoactive materials, the background photocurrent induced by semiconductor itself dramatically decreases. OPs, as a specific inhibitor for AChE activity, can prevent the generation of TCh and the dissociation of MnO₂ nanosheets, building a relationship between OPs concentration and photocurrent. Under the optimized test conditions, the PEC sensor for the detection of paraoxon displays a wide linear range from 0.05 to 10 ng/mL with a detection limit of 0.017 ng/mL. Furthermore, the PEC sensor shows good sensitivity, stability, and promising application in practical samples.

Nanostructured MoO3 for Efficient Energy and Environmental Catalysis

This paper mainly focuses on the application of nanostructured MoO₃ materials in both energy and environmental catalysis fields. MoO₃ has wide tunability in bandgap, a unique semiconducting structure, and multiple valence states. Due to the natural advantage, it can be used as a high-activity metal oxide catalyst, can serve as an excellent support material, and provide opportunities to replace noble metal catalysts, thus having broad application prospects in catalysis. Herein, we comprehensively summarize the crystal structure and properties of nanostructured MoO₃ and highlight the recent significant research advancements in energy and environmental catalysis. Several current challenges and perspective research directions based on nanostructured MoO₃ are also discussed.

Rationally Engineered Photonic-Plasmonic Synergistic Resonators in Second Near-Infrared Window for in Vivo Photoelectrochemical Biodetection

The introduction of photonic technologies into biodetection fields is in high demand to accelerate understanding vital movements at the molecular level. Great difficulty lies in the fact that the short penetration of photons in biotissues limits the practical applications of in vivo biodetection. Herein, we overcome this long-standing technical challenge through first introducing a new synergistic photonic-plasmonic resonator in second near-infrared window to realize efficient light trapping in this "bio-transparent zone". The well-match of photonic and plasmonic resonances in the same wavelength significantly increases the light-matter interplay activity, with 60% increase of quality factors, thus allowing us to pioneeringly implement the sensitive photoelectrochemical in vivo biodetection of macrophage cells in the tail vein of a living mouse. These synergistic photonic-plasmonic resonators promise bridges between vital photonic phenomena and practical biodetections or clinical applications.

Three-dimensional CdS nanosheet-enwrapped carbon fiber framework: Towards split-type CuO-mediated photoelectrochemical immunoassay

This work reports a customized methodology for the fabrication of 3D CdS nanosheet (NS)-enwrapped carbon fiber framework (CFF) and its utilization for sensitive split-type CuO-mediated PEC immunoassay. Specifically, the 3D CdS NS-CFF was fabricated via a solvothermal process, while the sandwich immunocomplexing was allowed in a 96 well plate with CuO nanoparticles (NPs) as the signaling labels. The subsequent release of the Cu²⁺ ions was directed to interact with the CdS NS, generating trapping sites and thus inhibiting its photocurrent generation. In such a protocol, the 3D CdS NS-CFF photoelectrode could not only guarantee its sufficient contact with the Cu²⁺-containing solution but also supply plenty CdS surface for the Cu²⁺ ions. Because of the target-dependent release of the Cu²⁺ ions and its proper coupling with the 3D CdS NS-CFF photoelectrode, a sensitive split-type PEC immunoassay was achieved for the detection of brain natriuretic peptide (BNP). This proposed system exhibited good stability and selectivity, and its applicability for real sample analysis was also demonstrated via comparison with the commercial BNP enzyme-linked immunosorbent assay (ELISA) kit. We expect this work could stimulate more interest in the design and utilization of 3D photoelectrodes for novel PEC bioanalysis.

Affinity-Based Detection of Biomolecules Using Photo-Electrochemical Readout

Detection and quantification of biologically-relevant analytes using handheld platforms are important for point-of-care diagnostics, real-time health monitoring, and treatment monitoring. Among the various signal transduction methods used in portable biosensors, photoelectrochemcial (PEC) readout has emerged as a promising approach due to its low limit-of-detection and high sensitivity. For this readout method to be applicable to analyzing native samples, performance requirements beyond sensitivity such as specificity, stability, and ease of operation are critical. These performance requirements are governed by the properties of the photoactive materials and signal transduction mechanisms that are used in PEC biosensing. In this review, we categorize PEC biosensors into five areas based on their signal transduction strategy: (a) introduction of photoactive species, (b) generation of electron/hole donors, (c) use of steric hinderance, (d) in situ induction of light, and (e) resonance energy transfer. We discuss the combination of strengths and weaknesses that these signal transduction systems and their material building blocks offer by reviewing the recent progress in this area. Developing the appropriate PEC biosensor starts with defining the application case followed by choosing the materials and signal transduction strategies that meet the application-based specifications.

Three-Dimensional TiO2@Cu2O@Nickel Foam Electrodes: Design, Characterization, and Validation of O2-Independent Photocathodic Enzymatic Bioanalysis

This work reports the innovative design and application of a three-dimensional (3D) TiO₂@Cu₂O@nickel foam electrode synergized with enzyme catalysis toward the proof-of-concept study for oxygen-independent photocathodic enzymatic detection. Specifically, a 3D-nanostructured photoelectrode has great potential in the semiconductor-based photoelectrochemical (PEC) biological analysis. On the other hand, using various photocathodes, cathodic PEC bioanalysis, especially the photocathodic enzymatic detection, represents an attractive frontier in the field. Different from state-of-the-art photocathodic enzymatic studies that are oxygen-dependent, herein, we present the ingenious design, characterization, and implementation of 3D TiO₂@Cu₂O@nickel foam photocathodes for the first oxygen-independent example. In such a configuration, the Cu₂O acted as the visible-light absorber, while the TiO₂ shell would simultaneously function as a protective layer for Cu₂O and as a desirable substrate for the immobilization of enzyme biomolecules. Especially, because of the proper band positions, the as-designed photocathode exhibited unique O₂-independent PEC property. Exemplified by glucose oxidases, the as-developed sensor exhibited positive response to glucose with good performance. Because various oxidases could be integrated with the system, this protocol could serve as a universal O₂-independent platform for many other targets. This work is also anticipated to catalyze more studies in the advanced 3D photoelectrodes toward innovative enzymatic applications.

Overview of RAW264.7 for osteoclastogensis study: Phenotype and stimuli

Bone homeostasis is preserved by the balance of maintaining between the activity of osteogenesis and osteoclastogenesis. However, investigations for the osteoclastogenesis were hampered by considerable difficulties associated with isolating and culturing osteoclast in vivo. As the alternative, stimuli‐induced osteoclasts formation from RAW264.7 cells (RAW‐OCs) have gain its importance for extensively osteoclastogenic study of bone diseases, such as rheumatoid arthritis, osteoporosis, osteolysis and periodontitis. However, considering the RAW‐OCs have not yet been well‐characterized and RAW264.7 cells are polymorphic because of a diverse phenotype of the individual cells comprising this cell linage, and different fate associated with various stimuli contributions. Thus, in present study, we provide an overview for current knowledge of the phenotype of RAW264.7 cells, as well as the current understanding of the complicated interactions between various stimuli and RAW‐OCs in the light of the recent progress.

One-Pot Synthesis of N-Graphene Quantum Dot-Functionalized I-BiOCl Z-Scheme Cathodic Materials for "Signal-Off" Photoelectrochemical Sensing of Chlorpyrifos

A Z-scheme I-BiOCl/N-GQD (i.e., nitrogen-doped graphene quantum dot) heterojunction was prepared by a one-pot precipitation method at room temperature. The doped iodine decreased the band gap of BiOCl, the introduced N-GQDs enhanced light harvesting and prolonged the photogenerated electron lifetime, and the resultant Z-scheme heterojunction promoted the spatial separation of interfacial charges. Thus, the composite showed high photoelectrochemical activity and a big cathodic photocurrent signal. On the basis of the coordination of chlorpyrifos with surface Bi(III) of the composite, a cathodic photoelectrochemical sensor was constructed for the selective detection of chlorpyrifos. In this case, chlorpyrifos decreased the lifetime of photogenerated electrons, so the photocurrent became small. Furthermore, the photocurrent changed and the logarithm of chlorpyrifos concentration presented a linear relationship. The linear range was 0.3-80 ng mL^-1, and the limit of detection was estimated to be 0.01 ng mL^-1 (defined as S/N = 3). The present strategy can also be used for the design and fabrication of other PEC sensors suitable for different analytes.

A Sunlight Powered Portable Photoelectrochemical Biosensor Based on a Potentiometric Resolve Ratiometric Principle

As a new analysis tool, photoelectrochemical (PEC) biosensors have been widely studied in recent years. However, common PEC biosensors usually require a highly stable light source to excite the electrical signal and an electrochemical workstation to collect and process the signal data, which limited the development of portable PEC devices. Herein, we propose the design of a sunlight powered portable PEC biosensor that uses sunlight as the light source. The sunlight intensity changes over time and weather and results in varied background PEC currents. To eliminate the interference caused by unstable excitation light, the potentiometric resolve ratiometric principle was introduced. Coupled with a miniature electrochemical workstation and a laptop, a sensitive and portable PEC sensing platform was successfully developed. The detection may be achieved under the irradiation of sunlight and will no longer need an extra light source. In a proof of concept experiment, this platform was successfully applied in aflatoxin B1 analysis, which was promising in the development of portable biosensors.

Metal-Free All-Carbon Nanohybrid for Ultrasensitive Photoelectrochemical Immunosensing of alpha-Fetoprotein

C₆₀ can accept up to six electrons reversibly and show exceptional light absorption over the entire UV-vis spectrum, making it a potential photoactive probe for photoelectrochemical (PEC) bioassay. However, few successful works have been reported to apply fullerenes in PEC biosensing, partially because of the low electronic conductivity and poor interfacial interactions with targeted biomolecules. Herein, we report the addressing of these two obstacles by coupling high conductive graphite flake (Gr), graphene oxide (GO) with sufficient oxygen-containing functional groups, and an alkylated C₆₀ (AC₆₀) into a metal-free all-carbon nanohybrid (AC₆₀-Gr-GO) via harnessing delicate noncovalent interactions among them through a facile mechanical grinding. It was revealed that the as-obtained AC₆₀-Gr-GO nanohybrid not only showed conspicuous enhancement of photocurrent up to 35 times but also offered rich anchors for bioconjugation. With detection of alpha-fetoprotein as an example, the AC₆₀-Gr-GO based PEC immunosensor demonstrated a broad linear detection range (1 pg·mL^-1 to 100 ng·mL^-1) and a detection limit as low as 0.54 pg·mL^-1, superior/competitive to PEC immunosensors for AFP in previous reports. By a proper reinforcement in conductivity and biointerface engineering, this work may provide a new way to use fullerenes as photoactive materials in more general PEC biosensing.

A DNA nanostructured aptasensor for the sensitive electrochemical detection of HepG2 cells based on multibranched hybridization chain reaction amplification strategy

Sensitive detection of cancer cells is beneficial to the early diagnosis of cancer and individual treatment. In the present study, a DNA nanostructured aptasensor was used for the sensitive electrochemical detection of human liver hepatocellular carcinoma cells (HepG2) based on multibranched hybridization chain reaction amplification strategy. We established a well-designed platform by immobilizing DNA tetrahedron, a three-dimensional DNA nanostructure, on the gold electrode to capture HepG2 cells more specifically and efficiently. Meanwhile, functional hybrid nanoprobes consisted of MIL-101@AuNPs (Au nanoparticles), numerous hemin/G-quadruplex DNAzyme from multibranched hybridization chain reaction, and natural horseradish peroxidase (HRP) was designed. The hybrid nanoprobes possessed the functions of specific discernment and enzymatic signal amplification simultaneously. With the help of nanoprobes, HepG2 cells were recognized and captured to form a DNA tetrahedron-cell-nanoprobe sandwich-like structure on the electrode surface. The lower detection limit of this established cytosensor is 5 cells per ml. Moreover, it delivered a broad detection range from 10² to 10⁷ cells per ml. The results revealed that the as-proposed cytosensor may be utilized as a powerful tool for early diagnosis of cancer in the future.

Conjugated Polymer-Based Photoelectrochemical Cytosensor with Turn-On Enable Signal for Sensitive Cell Detection

In this work, a new photoelectrochemical (PEC) cytosensor was constructed by using cationic polyfluorene derivative, poly(9,9-bis(6'-(N,N,N,-trimethylammonium)hexyl)fluorene-co-alt-1,4-phenylene)bromide (PFP) as the photoelectric-responsive material for sensitive cell detection. Positive-charged PFP with high photoelectric conversion efficiency can generate robust photocurrent under light illumination. In the PEC cytosensor, 3-phosphonopropionic acid was linked to the indium tin oxide electrode, followed by modification with antiepithelial-cell-adhesion-molecule (EpCAM) antibody via amide condensation reaction. Thus, target SKBR-3 cells with overexpressed EpCAM antigen could be captured onto the electrode via the specific antibody-antigen interactions. Upon adding cationic PFP, a favorable electrostatic interaction between cationic PFP and negatively charged cell membrane led to a turn-on detection signal for target SKBR-3 cells. This new cytosensor not only exhibits good sensitivity because of the good photoelectric performance of conjugated polymers, but also offers decent selectivity to target cells by taking advantage of the specific antibody-antigen recognition.

Bismuth Oxyiodide Couples with Glucose Oxidase: A Special Synergized Dual-Catalysis Mechanism for Photoelectrochemical Enzymatic Bioanalysis

On the basis of a special synergized dual-catalysis mechanism, this work reports the preparation of a BiOI-based heterojunction and its use for cathodic photoelectrochemical (PEC) oxidase biosensing, which, unexpectedly, revealed that hydrogen peroxide (H₂O₂) had a greater impact than dioxygen (O₂). Specifically, the BiOI layer was in situ formed on the substrate through an impregnating hydroxylation method for the following coupling with the model enzyme of glucose oxidases (GOx). The constructed cathodic PEC enzyme sensor exhibited a good analytical performance of rapid response, high stability, and good selectivity. Especially, glucose-induced H₂O₂-controlled enhancement of the photocurrent was recorded rather than the commonly observed O₂-dependent suppression of the signal. This interesting phenomenon was attributed to a special synergized dual-catalysis mechanism. Briefly, this study is expected to provide a new BiOI-based photocathode for general PEC bioanalysis development and to inspire more interest in the design and construction of a novel heterojunction for advanced photocathodic bioanalysis. More importantly, the mechanism revealed here would offer a totally different perspective for the use of a biomimetic catalyst in the design of future PEC enzymatic sensing and the understanding of relevant signaling routes as well as the implementation of innovative PEC devices.

A ratiometric photoelectrochemical immunosensor based on g-C3N4@TiO2 NTs amplified by signal antibodies–Co3O4 nanoparticle conjugates

Herein, we report a ratiometric photoelectrochemical (PEC) immunosensor coupled with secondary antibodies–Co₃O₄ nanoparticle conjugates (Ab₂–Co₃O₄ NPs) for signal amplification.