CdS Quantum-Dots-Decorated V2O5 Nanosheets as Chemically Etchable Active Materials for Sensitive Photoelectrochemical Immunoassay of Carcinoembryonic Antigen

Carbon Nanotube Field-Effect Transistor Biosensor with an Enlarged Gate Area for Ultra-Sensitive Detection of a Lung Cancer Biomarker

Carcinoembryonic antigen (CEA) is a recognized biomarker for lung cancer and can be used for early detection. However, the clinical value of CEA is not fully realized due to the rigorous requirement for high-sensitivity and wide-range detection methods. Field-effect transistor (FET) biosensors, as one of the potentially powerful platforms, may detect CEA with a significantly higher sensitivity than conventional clinical testing equipment, while their sensitivity and detection range for CEA are far below the requirement for early detection. Here, we construct a floating gate FET biosensor to detect CEA based on a semiconducting carbon nanotube (CNT) film combined with an undulating yttrium oxide (Y₂O₃) dielectric layer as the biosensing interface. Utilizing an undulating biosensing interface, the proposed device showed a wider detection range and optimized sensitivity and detection limit, which benefited from an increase of probe-binding sites on the sensing interface and an increase of electric double-layer capacitance, respectively. The outcomes of analytical studies confirm that the undulating Y₂O₃ provided the desired biosensing surface for probe immobilization and performance optimization of a CNT-FET biosensor toward CEA including a wide detection range from 1 fg/mL to 1 ng/mL, good linearity, and high sensitivity of 72 ag/mL. More crucially, the sensing platform can function normally in the complicated environment of fetal bovine serum, indicating its great promise for early lung cancer screening.

Highly sensitive photoelectrochemical immunosensor for detecting cancer marker CA19-9 based on a new SnSe quantum dot

A sandwich-type photoelectrochemical (PEC) immunosensor was constructed on a screen-printed electrode (SPE) using gold-coated tin selenide quantum dots (Au-SnSe QDs) to determine the carbohydrate antigen 19 9 (CA19-9). Water-soluble Au-SnSe QDs were prepared by coating low-cost SnSe QDs, prepared by reacting tin(II) 2-ethyl hexanoate with selenium ions (HNaSe) without needing to add an external capping agent (SnSe QDs). SnSe-based QDs were characterized using high-resolution transmission electron microscopy (HR-TEM) and dynamic light scattering (DLS). DSP (dithio-bis (succinimidyl propionate)) as a linker was attached on Au@SnSe QDs and conjugated with CA19-9 monoclonal antibodies (Ab₂-DSP-Au@SnSE QD). For capture probe assembling, an Au nano-layer was electrochemically deposited on a SPE by HAuCl₄ reduction using 12 cycles of cyclic voltammetry (0 to - 1.4 V) at the scan rate of 50 mV s^-1, then covered by self-assembly of DSP and covalent conjugation of CA19-9 Ab₁. Our developed PEC immunosensor showed a significant photoelectrochemical response, recorded using chronoamperometry (0.3 V), for the presence of CA19-9 antigen in serum samples under light irradiation, with a detection limit (LOD) of 0.0011 U mL^-1 and a dynamic range of 0.005-100 U mL^-1. The recovery of CA19-9 determination from serum samples was 101 to 113%.

A Novel Signaling Strategy for an Ultrasensitive Photoelectrochemical Immunoassay Based on Electro-Fenton Degradation of Liposomes on a Photoelectrode

A signaling strategy can directly determine the analytical performance and application scope of photoelectrochemical (PEC) immunoassays, so it is of great significance to develop an effective signaling strategy. The electro-Fenton reaction has been extensively used to degrade organic pollutants, but it has not been applied to PEC immunoassays. Herein, we report a novel signaling strategy for a PEC immunoassay based on electro-Fenton degradation of liposomes (Lip) on a photoelectrode. Lip vesicles are coated on Au@TiO₂ core-shell photoactive material, which can prevent ascorbic acid (AA) from scavenging photogenerated holes. In the presence of a target, the immunomagnetic bead labels are converted to Fe³⁺ for electro-Fenton reaction, and hydroxyl radicals generated by the electro-Fenton reaction can degrade the Lip vesicles on the photoelectrode. Because of the degradation of Lip vesicles, photogenerated holes can be scavenged more effectively by AA, leading to an increase in photocurrent. Based on the electro-Fenton-regulated interface electron transfer, the sensitive "signal on" PEC immunoassay of a carcinoembryonic antigen is achieved, which features a dynamic range from 0.05 to 5 × 10⁴ pg mL^-1 and a detection limit of 0.01 pg mL^-1. Our work provides a novel and efficient PEC immunoassay platform by introducing the electro-Fenton reaction into PEC analysis.

Photoelectrochemical detection of microRNAs based on target-triggered self-assembly of energy band position-matched CdS QDs and C3N4 nanosheets

An ultrasensitive photochemical biosensor based on the target miRNA-triggered catalytic hairpin assembly (CHA) reaction between Au nanoparticles (AuNPs)/C₃N₄ nanosheets and CdS quantum dots (QDs) was developed for the determination of miRNAs. Firstly, AuNPs/C₃N₄ nanosheets were immobilized onto a working glassy carbon electrode. Then, the hairpin probe 1 (H1) was loaded through Au-S bonding. Afterward, the unbound sites were blocked with 6-mercaptohexanol to avoid nonspecific adsorption. In the presence of the target miRNA, the CHA reaction between the H1 and hairpin probe 2-CdS QDs (H2-CdS QDs) could be triggered. As a result, the AuNPs/C₃N₄ nanosheet and CdS QDs were linked by the double helix structure H1-H2. Unlike the other CHA reactions, H2 used in this work is longer than H1 so that the AuNPs/C₃N₄ nanosheets could touch the CdS QDs. Given the matched energy band positions between the C₃N₄ nanosheet and CdS QDs, a strong photocurrent could be obtained after the CHA reaction was triggered by the target miRNA. In addition, p-type C₃N₄ nanosheets and n-type CdS QDs presented reduction photocurrents and oxidation photocurrents, respectively. Therefore, the photocurrents were vectors in this design that can eliminate the interference of nonspecific adsorption and avoid the generation of false-positive signals. Under the optimal conditions, the limit of detection was 92 aM. The constructed photoelectrochemical biosensor showed good reproducibility and selectivity in the analysis of serum samples, which indicates its great prospects in disease diagnostics and bioanalysis.

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.

Electrochemistry/Photoelectrochemistry-Based Immunosensing and Aptasensing of Carcinoembryonic Antigen

Recently, electrochemistry- and photoelectrochemistry-based biosensors have been regarded as powerful tools for trace monitoring of carcinoembryonic antigen (CEA) due to the fact of their intrinsic advantages (e.g., high sensitivity, excellent selectivity, small background, and low cost), which play an important role in early cancer screening and diagnosis and benefit people's increasing demands for medical and health services. Thus, this mini-review will introduce the current trends in electrochemical and photoelectrochemical biosensors for CEA assay and classify them into two main categories according to the interactions between target and biorecognition elements: immunosensors and aptasensors. Some recent illustrative examples are summarized for interested readers, accompanied by simple descriptions of the related signaling strategies, advanced materials, and detection modes. Finally, the development prospects and challenges of future electrochemical and photoelectrochemical biosensors are considered.

Tailoring the Photoelectrochemical Activity of Hexametaphosphate-Capped CdS Quantum Dots by Ca2+-Triggered Surface Charge Regulation: A New Signaling Strategy for Sensitive Immunoassay

The development of efficient signaling strategies is highly important for photoelectrochemical (PEC) immunoassay. We report here a new and efficient strategy for sensitive PEC immunoassay by tailoring the electrostatic interaction between the photoactive material and the electron donor. The photoelectric conversion of hexametaphosphate (HMP)-capped CdS quantum dots (QDs) in Na₂SO₃ solution is significantly boosted after Ca²⁺ incubation. The negative surface charges on CdS@HMP QDs decrease because of the complexation reaction between HMP and Ca²⁺, and the electrostatic repulsion between CdS@HMP QDs and electron donor (SO₃^2-) becomes weak accordingly, leading to an improved electron-hole separation efficiency. Inspired by the PEC response of CdS@HMP QDs to Ca²⁺, a novel "signal-on" PEC immunoassay platform is established by employing CaCO₃ nanoparticles as labels. By regulating the surface charge of CdS@HMP QDs with in situ-generated Ca²⁺ from CaCO₃ labels, sensitive detection of the carcinoembryonic antigen (CEA) is achieved. The linear detection range is 0.005-50 ng mL^-1 and the detection limit is 1 pg mL^-1 for CEA detection. Our work not only provides a facile route to tailor the photoelectric conversion but also lays the foundation for sensitive PEC immunoassay by simply regulating the surface charge of photoactive materials.

Prevent or Cure-The Unprecedented Need for Self-Reporting Materials

Self-reporting smart materials are highly relevant in modern soft matter materials science, as they allow for the autonomous detection of changes in synthetic polymers, materials, and composites. Despite critical advantages of such materials, for example, prolonged lifetime or prevention of disastrous material failures, they have gained much less attention than self-healing materials. However, as diagnosis is critical for any therapy, it is of the utmost importance to report the existence of system changes and their exact location to prevent them from spreading. Thus, we herein critically review the chemistry of self-reporting soft matter materials systems and highlight how current challenges and limitations may be overcome by successfully transferring self-reporting research concepts from the laboratory to the real world. Especially in the space of diagnostic self-reporting systems, the recent SARS-CoV-2 (COVID-19) pandemic indicates an urgent need for such concepts that may be able to detect the presence of viruses or bacteria on and within materials in a self-reporting fashion.

Ultrasensitive DNA Detection Based on Inorganic-Organic Nanocomposite Cosensitization and G-Quadruplex/Hemin Catalysis for Signal Amplification

A novel photoelectrochemical (PEC) aptasensor was fabricated for DNA detection based on the coupling of cosensitization and peroxidase-like catalytic activity. Specifically, the surfaces of branched-TiO₂ nanorods (B-TiO₂ NRs) were modified with Cd²⁺ and S²⁺ to obtain B-TiO₂ NRs/CdS hybrid structures, which were subsequently used as matrices to immobilize hairpin DNA (hDNA) probes. CdTe/TCPP (TCPP = meso-tetra(4-carboxyphenyl)-porphine) used for signal amplification was labeled on the terminal of the hDNA probe. Without the target DNA (tDNA) presence, the immobilized hDNA probe with CdTe/TCPP possessed a hairpin form and was located near the B-TiO₂ NRs/CdS electrode surface, forming a cosensitized structure formation and then generating strong photocurrent with H₂O₂ as the electron donor. During detection, the specific recognition of tDNA by the sensing hDNA probe triggered the formation of the G-quadruplex/hemin DNAzyme, which effectively catalyzed the decomposition of H₂O₂. Meanwhile, cosensitization disappeared when the hDNA probe hybridized with tDNA, further reducing the photocurrent. With a double-signal amplification strategy, the sensing platform designed in this work demonstrated a linear detection ability in the 0.5 fM-5 nM range with a detection limit equal to 0.14 fM. Notably, through encoding in the base sequences of the hDNA and marking it, a versatile PEC platform could be structured for the detection of various DNA targets, which could promise applications in point-of-care diagnostic fields.