Photoelectrochemical immunosensor based on CdSe@BiVO4 Co-sensitized TiO2 for carcinoembryonic antigen

Signal amplification strategies in photoelectrochemical sensing of carcinoembryonic antigen

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

Triblock polyadenine-based electrochemical aptasensor for ultra-sensitive detection of carcinoembryonic antigen via exonuclease III-assisted target recycling and hybridization chain reaction

Carcinoembryonic antigen (CEA), a key colon biomarker, demands a precise detection method for cancer diagnosis and prognosis. This study introduces a novel electrochemical aptasensor using a triblock polyadenine probe for ultra-sensitive detection of CEA. The method leverages Exonuclease III (Exo III)-assisted target recycling and hybridization chain reaction. The triblock polyadenine probe self-assembles on the bare gold electrode through the strong affinity between adenine and gold electrode, blocking CEA diffusion and providing a large immobilization surface. CEA binding to hairpin probe 1 (HP1), followed by the hybridization between HP1 and hairpin probe 2 (HP2), triggers DNA cleavage by Exo III, amplifying the signal via a hybridization chain reaction and producing numerous dsDNA walkers that generates a dramatic electrochemical impedance signal. Under optimized conditions, the aptasensor achieved two ultra-low detection limits: 0.39 ag∙mL-1 within the concentration range of 5 ag∙mL-1 to 5 × 106 ag∙mL-1, and 1.5 ag∙mL-1 within the concentration range of 5 × 106 ag∙mL-1 to 1 × 1010 ag∙mL-1. Its performance in human serum samples meets the practical standards, offering a promising new tool for ultrasensitive tumor marker detection, potentially revolutionizing early cancer diagnosis.

Smartphone-based photoelectrochemical immunoassay for carcinoembryonic antigen based on BiOCl/CuBi2O4 heterojunction

Photoelectrochemical (PEC) immunoassay has been widely developed for biomarker detection, but most include heavy and expensive instruments that are not suited for portable and on-site detection. In this work, the PEC immunoassay platform for mobile phones was reported for flexible, rapid, low-cost detection of carcinoembryonic antigen (CEA). The PEC detection platform was successfully composed of disposable screen-printed carbon electrodes, a micro-electrochemical workstation, a flashlight (the excitation light source), and a smartphone with a companion software with a micro-electrochemical workstation for rapid and on-site detection of target biomarkers. In this portable smartphone-based PEC system, the S-scheme heterojunction BiOCl/CuBi2O4 was effectively excited due to the efficient electron transfer rate and excellent photocurrent response under visible light. Specifically, the sandwich-type immunoreaction for capturing target biomarkers introduced alkaline phosphatase (ALP) labeled gold nanoparticles (Au NPs). The addition of CEA increased the ascorbic acid (AA) content and enhanced the photocurrent. The proposed immunoassay presented a good linear with the logarithm of CEA concentrations range within 0.01-40 ng mL-1, and the detection limit of 3.5 pg mL-1 (S/N = 3). Therefore, the portable detection platform offered an implementable approach to the development of miniaturized and portable photoelectrochemical detectors and on-site detection technology.

2D Piezoelectric BiVO4 Artificial Nanozyme with Adjustable Vanadium Vacancy for Ultrasound Enhanced Piezoelectric/Sonodynamic Therapy

Increasing the yield of reactive oxygen species (ROS) to enhance oxidative stress in cells is an eternal goal in cancer therapy. In this study, BiVO4 artificial nanozyme is developed with adjustable vanadium vacancy for ultrasound (US) enhanced piezoelectric/sonodynamic therapy. Under US excitation, the vanadium vacancy-rich BiVO4 nanosheets (abbreviated Vv -r BiVO4 NSs) facilitate the generation of a large number of electrons to improve the ROS yield. Meanwhile, the mechanical strain imposed by US irradiation makes the Vv -r BiVO4 NSs display a typical piezoelectric response, which tilts the conduction band to be more negative and the valance band more positive than the redox potentials of O2 /O2 •- and H2 O/·OH, boosting the efficiency of ROS generation. Both density functional theory calculations and experiments confirm that the introduction of cationic vacancy can improve the sonodynamic effect. As expected, Vv -r BiVO4 NSs have better peroxidase enzyme catalytic and glutathione depletion activities, resulting in increased intracellular oxidative stress. This triple amplification strategy of oxidative stress induced by US substantially inhibits the growth of cancer cells. The work may open an avenue to achieve a synergetic therapy by introducing cationic vacancy, broadening the biomedical use of piezoelectric materials.

Ultrasensitive MicroRNA Photoelectric Assay Based on a Mimosa-like CdS-NiS/Au Schottky Junction

Seeking and constructing superior photoactive materials have the potential to improve the performance of photoelectrochemical (PEC) biosensors. In this work, we proposed a novel mimosa-like ternary inorganic composite with a significantly enhanced light-harvesting ability and photogenerated carrier separation rate. This ternary photoactive material was obtained via electrodeposition of gold nanoparticles (Au) on the surface of transition metal sulfide composite of CdS and NiS (CdS-NiS/Au). The experimental results showed that the high initial photocurrent was acquired on CdS-NiS/Au (68-fold higher than that of individual CdS) with the synergistic effect of p-n heterojunction, Schottky junction, and the eminent optical properties of gold nanoparticles. Meanwhile, using silver nanoclusters prepared by link DNA protection as an effective quencher, integrating the duplex-specific nuclease-assisted rolling circle amplification strategy, a "Signal ON" PEC biosensor was fabricated for the detection of microRNA 21 (miRNA 21). With the release of the quencher, the recovered photocurrent is able to achieve determination of miRNA 21 within the range from 10 aM to 1 pM with a detection limit down to 4.6 aM (3σ). Importantly, this work not only provides a superb idea for designing ternary inorganic heteromaterials with exceptional photoactive ability but also allows the detection of other biomarkers by selecting appropriate recognition units.

C-doped ZnO nanocomposites molecularly imprinted photoelectrochemical sensor for ultrasensitive and selective detection of oxytetracycline in milk

Antibiotic monitoring remains vital to ensure human health and safety in the environment and foods. As the most popular detection method, photoelectrochemical (PEC) sensor can achieve rapid and accurate detection of antibiotics with the advantages of high sensitivity, easy-to-preparation process, as well as high selectivity. Herein, an extremely-efficient visible-light responsible ZnO/C nanocomposite was prepared and combined with acetylene black (as an enhanced conductive matrix), and the electron migration efficiency was greatly accelerated. Meanwhile, a molecularly imprinted polymer obtained by electrical agglomeration was conjugated as a specific recognizing site for target. Furthermore, the as-prepared rMIP-PEC sensor showed a low detection limit (8.75 pmol L^-1, S/N = 3) in a wide linear detection range of 0.01-1000 nmol L^-1 for oxytetracycline (OTC), with excellent selectivity and long-term stability. Our work shed light on applying C-doped ZnO semiconductor and molecularly imprinted polymer as photoelectric active sensing materials for rapid and accurate analysis of antibiotics in foods and environment.

Electrochemical and Photoelectrochemical Immunosensors for the Detection of Ovarian Cancer Biomarkers

Photoelectrochemical (PEC) sensing is an emerging technological innovation for monitoring small substances/molecules in biological or non-biological systems. In particular, there has been a surge of interest in developing PEC devices for determining molecules of clinical significance. This is especially the case for molecules that are markers for serious and deadly medical conditions. The increased interest in PEC sensors to monitor such biomarkers can be attributed to the many apparent advantages of the PEC system, including an enhanced measurable signal, high potential for miniaturization, rapid testing, and low cost, amongst others. The growing number of published research reports on the subject calls for a comprehensive review of the various findings. This article is a review of studies on electrochemical (EC) and PEC sensors for ovarian cancer biomarkers in the last seven years (2016-2022). EC sensors were included because PEC is an improved EC; and a comparison of both systems has, expectedly, been carried out in many studies. Specific attention was given to the different markers of ovarian cancer and the EC/PEC sensing platforms developed for their detection/quantification. Relevant articles were sourced from the following databases: Scopus, PubMed Central, Web of Science, Science Direct, Academic Search Complete, EBSCO, CORE, Directory of open Access Journals (DOAJ), Public Library of Science (PLOS), BioMed Central (BMC), Semantic Scholar, Research Gate, SciELO, Wiley Online Library, Elsevier and SpringerLink.

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.

2D carbon materials based photoelectrochemical biosensors for detection of cancer antigens

Cancer is a leading cause of death globally and early diagnosis is of paramount importance for identifying appropriate treatment pathways to improve cancer patient survival. However, conventional methods for cancer detection such as biopsy, CT scan, magnetic resonance imaging, endoscopy, X-ray and ultrasound are limited and not efficient for early cancer detection. Advancements in molecular technology have enabled the identification of various cancer biomarkers for diagnosis and prognosis of the deadly disease. The detection of these biomarkers can be done by biosensors. Biosensors are less time consuming compared to conventional methods and has the potential to detect cancer at an earlier stage. Compared to conventional biosensors, photoelectrochemical (PEC) biosensors have improved selectivity and sensitivity and is a suitable tool for detecting cancer agents. Recently, 2D carbon materials have gained interest as a PEC sensing platform due to their high surface area and ease of surface modifications for improved electrical transfer and attachment of biorecognition elements. This review will focus on the development of 2D carbon nanomaterials as electrode platform in PEC biosensors for the detection of cancer biomarkers. The working principles, biorecognition strategies and key parameters that influence the performance of the biosensors will be critically discussed. In addition, the potential application of PEC biosensor in clinical settings will also be explored, providing insights into the future perspective and challenges of exploiting PEC biosensors for cancer diagnosis.

A Sensitive Photoelectrochemical Sensor for Levodopa Detection Using Benzothiadiazole-Based Conjugated Microporous Polymer-Coated Graphene Heterostructures

Since the 1960s, levodopa (LDA) has been the standard drug for treating of Parkinson's disease. In this study, a novel benzothiadiazole-based conjugated microporous polymer-coated graphene heterostructure (CMP-rGO) was synthesized and used to construct a sensitive photoelectrochemical (PEC) sensor capable of detecting LDA. Under optimal experimental conditions, the intensity of the photocurrent produced by the sensor was linear from 0.005 to 40 μM, and the limit of detection of the sensor was 0.0027 μM. The sensor showed good repeatability, stability, and selectivity for LDA detection. Finally, the constructed sensor was used to detect LDA in levodopa tablets, human serum samples, and urine samples and satisfactory results were obtained. Therefore, the PEC sensor provides a novel platform for the detection of LDA in real samples and broadens the applications of conjugated microporous polymers in PEC sensing.

Electrochemical α-fetoprotein immunosensor based on Fe3O4NPs@covalent organic framework decorated gold nanoparticles and magnetic nanoparticles including SiO2@TiO2

The early diagnosis of major diseases such as cancer is typically a major issue for humanity. Human α-fetoprotein (AFP) as a sialylated glycoprotein is of approximately 68 kD molecular weight and is considered to be a key biomarker, and an increase in its level indicates the presence of liver, testicular, or gastric cancer. In this study, an electrochemical AFP immunosensor based on Fe₃O₄NPs@covalent organic framework decorated gold nanoparticles (Fe₃O₄ NPs@COF/AuNPs) for the electrode platform and double-coated magnetic nanoparticles (MNPs) based on SiO₂@TiO₂ (MNPs@SiO₂@TiO₂) nanocomposites for the signal amplification was fabricated. The immobilization of anti-AFP capture antibody was successfully performed on Fe₃O₄ NPs@COF/AuNPs modified electrode surface by amino-gold affinity, while the conjugation of anti-AFP secondary antibody on MNPs@SiO₂@TiO₂ was achieved by the electrostatic/ionic interactions. Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) analysis, cyclic voltammetry (CV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS) techniques were used to characterize the nanostructures in terms of physical and electrochemical features. The limit of detection (LOD) was 3.30 fg mL^-1. The findings revealed that the proposed electrochemical AFP immunosensor can be effectively used to diagnose cancer.

Immunoassay technology: Research progress in microcystin-LR detection in water samples

Increasing global warming and eutrophication have led to frequent outbreaks of cyanobacteria blooms in freshwater. Cyanobacteria blooms cause the death of aquatic and terrestrial organisms and have attracted considerable attention since the 19th century. Microcystin-LR (MC-LR) is one of the most typical cyanobacterial toxins. Therefore, the fast, sensitive, and accurate determination of MC-LR plays an important role in the health of humans and animals. Immunoassay refers to a method that uses the principle of immunology to determine the content of the tested substance in a sample using the tested substance as an antigen or antibody. In analytical applications, the immunoassay technology could use the specific recognition of antibodies for MC-LR detection. In this review, we firstly highlight the immunoassay detection of MC-LR over the past two decades, including classical enzyme-link immunosorbent assay (ELISA), modern immunoassay with optical signal, and modern immunoassay with electrical signal. Among these detection methods, the water environment was used as the main detection system. The advantages and disadvantages of the different detection methods were compared and analyzed, and the principles and applications of immunoassays in water samples were elaborated. Furthermore, the current challenges and developmental trends in immunoassay were systematically introduced to enhance MC-LR detection performance, and some critical points were given to deal with current challenges. This review provides novel insight into MC-LR detection based on immunoassay method.

A sandwich-type photoelectrochemical aptasensor using Au/BiVO4 and CdS quantum dots for carcinoembryonic antigen assay

A novel sandwich-type photoelectrochemical (PEC) aptasensor for the carcinoembryonic antigen (CEA) assay was fabricated using the CEA aptamer, Au/BiVO₄ and CdS quantum dots (CdS QDs). In virtue of the localized surface plasmon resonance effect of Au nanoparticles, Au/BiVO₄ showed an effective utilization of visible light and excellent photoactivity, and was employed as the photoanode. After CdS QDs were conjugated to Au/BiVO₄ through the sandwich structure based on the hybridization of the CEA aptamer with two partially complementary single-stranded DNA molecules, the photocurrents were further enhanced by a resonance energy transfer between CdS QDs and Au nanoparticles. Meanwhile, the consumption of the photo-induced holes by ascorbic acid could also retard the combination of the electron-hole pairs and cause an increase of the photocurrents. However, the specific recognition of CEA by the CEA aptamer could destroy the sandwich structure and remarkably weaken the photocurrent response. Thus, the quantitative detection of CEA was connected with the decrease of the photocurrent. Benefitting from the above methods for signal enhancement, the PEC aptasensor showed a wide sensing range of 0.0001-10 ng mL^-1 and a low detection limit of 0.047 pg mL^-1 for CEA detection. The specificity, stability and recoveries of the PEC aptasensor were also excellent. Therefore, the construction of the present PEC aptasensor provides a universal and practical method for sensing other substances.

Development of QDs-based nanosensors for heavy metal detection: A review on transducer principles and in-situ detection

Heavy metal pollution has severe threats to the ecological environment and human health. Thus, it is urgent to achieve the rapid, selective, sensitive and portable detection of heavy metal ions. To overcome the defects of traditional methods such as time-consuming, low sensitivity, high cost and complicated operation, QDs (Quantum dots)-based nanomaterials have been used in sensors to significantly improve the sensing performance. Due to their excellent physicochemical properties, high specific surface area, high adsorption and reactive capacity, nanomaterials could act as potential probes or offer enhanced sensitivity and create a promising nanosensors platform. In this review, the rapidly advancing types of QDs for heavy metal ions detection are first summarized. Modified with ligands, nanomaterials, or biomaterials, QDs are assembled on sensors by the interaction of electrostatic adsorption, chemical bonding, steric hindrance, and base-pairing. The stability of QDs-based nanosensors is improved by doping the elements to QDs, providing the reference substance, optimizing the assemble strategies and so on. Then, according to transducer principles, the two most typical sensor categories based on QDs: optical and electrochemical sensors are highlighted to be discussed. In the meanwhile, portable devices combining with QDs to adapt the practical detection in complex situations are summarized. The deficiencies and future challenges of QDs in toxicity, specificity, portability, multi-metal co-detection and degradation during the detection are also pointed out. In the end, the development trends of QDs-based nanosensors for heavy metal ions detection are discussed. This review presents an overall understanding, recent advances, current challenges and future outlook of QDs-based nanosensors for heavy metal detection.

Nanobody-based immunosensing methods for safeguarding public health

Immunosensing methods are biosensing techniques based on specific recognition of an antigen-antibody immunocomplex, which have become commonly used in safeguarding public health. Taking advantage of antibody-related biotechnological advances, the utilization of an antigen-binding fragment of a heavy-chain-only antibody termed as 'nanobody' holds significant biomedical potential. Compared with the conventional full-length antibody, a single-domain nanobody retaining cognate antigen specificity possesses remarkable physicochemical stability and structural adaptability, which enables a flexible and efficient molecular design of the immunosensing strategy. This minireview aims to summarize the recent progress in immunosensing methods using nanobody targeting tumor markers, environmental pollutants, and foodborne microbes.

Ultrasensitive photoelectrochemical immunoassay for prostate-specific antigen based on silver nanoparticle-triggered ion-exchange reaction with ZnO/CdS nanorods

Prostate-specific antigen (PSA), a glycoprotein that is most likely to cause prostate cancer, has attracted widespread attention in recent years due to its increasing threat to people's lives and health. Herein, we developed a new signal-amplified photoelectrochemical (PEC) immunosensing method for quantitative monitoring of the target PSA based on the ion-exchange reaction for the in situ formation of ZnO/CdS/Ag₂S nanohybrids triggered by the as-released silver ions (Ag⁺) from silver nanolabels. Initially, the introduction of a target PSA caused the formation of a sandwich immunocomplex in an anti-PSA capture antibody (cAb)-coated microplate with the help of a silver nanoparticle-labeled detection antibody (AgNPs-dAb). Thereafter, the introduced AgNPs were dissolved with acid to release numerous silver ions. In this regard, an ion-exchange reaction occurred between the silver ions and ZnO/CdS nanorods on the photosensitive electrode, thus producing ZnO/CdS/Ag₂S nanohybrids to generate a relatively strong photocurrent. Under optimal conditions, the ion-exchange reaction-based PEC immunoassay exhibited a good linear range of 0.05-50 ng mL^-1 and allowed the detection of the target PSA at a concentration as low as 0.018 ng mL^-1. In addition, the PEC immunoassay displayed satisfactory repeatability, high specificity, and acceptable method accuracy. Importantly, the ion-exchange reaction-based PEC immunoassay provides a new perspective for the detection of other disease-related biomarkers by controlling the corresponding antibodies.

A dual-signal self-checking photoelectrochemical immunosensor based on the sole composite of MIL-101(Cr) and CdSe quantum dots for the detection of α-fetoprotein

Designing a photoelectrochemical (PEC) immunosensor that can produce dual photocurrent signals which can refer to each other is a great importance but a big challenge. In this manuscript, a novel dual photocurrent signals immunosensor was constructed for the detection of α-fetoprotein (AFP). Unlike the usual method of using two composite materials to provide cathode and anode photocurrent respectively, this work applies only one compound of MIL-101 (Cr) and CdSe quantum dots (QDs). Thereinto, we found that the photocurrent polarity of MIL-101(Cr) would switch by adjusting applied voltage. And then CdSe QDs was introduced by simple ultrasound mixing to boost the dual photocurrent signals. Furthermore, in the composite of M&C, the electron transfer path between MIL-101(Cr) and CdSe QDs may switch between "Z-type" and "Ⅱ-type" by adjusting voltage. Benefiting by the dual signals, the proposed sensor can not only perform sensitively quantitative detection of α-fetoprotein (AFP), but also can intuitively estimate the accuracy and reliability of the test result by determining whether the corresponding relationship of "cathode photocurrent-analyte concentration-anode photocurrent" is established. The linear ranges of the sensing electrodes as cathode and anode are the same, both from 0.1 to 300 ng mL^-1. The limit of detection (LOD) is 0.082 ng mL^-1 (S/N = 3) when it used as an anode, and the LOD is 0.054 ng mL^-1 (S/N = 3) when it served as cathode. Furthermore, this sensor showed acceptable stability, reproducibility, specificity, and feasibility of detecting AFP in human serum, which has broad development prospects in the early clinical diagnosis.

Biocatalyst and colorimetric biosensor of carcinoembryonic antigen constructed via chicken egg white-copper phosphate organic/inorganic hybrid nanoflowers

In this article, the dual-functional chicken egg white-copper phosphate organic-inorganic hybrid nanoflowers (Cu-NFs), combining the functions of signal amplification and biological recognition, were prepared through a simple one-pot method. The Cu-NFs exhibit excellent biocatalytic activity of peroxidase and polyphenol oxidase. Besides, a biotin-labeled secondary antibody encapsulated Cu-NFs-2 (Cu-NFs-2@Biotin-NHS-Ab₂) capture probe was prepared by using the interaction between avidin in the egg white and biotin. Based upon this superiority, the as-prepared Cu-NFs-2 were used in labeled avidin-biotin enzyme-linked immunosorbent assay (Cu-NFs-2 based-LAB-ELISA) to construct a sensitive colorimetric biosensor for the ultrasensitive detection of carcinoembryonic antigen (CEA). Under weak alkaline (pH = 7.5) conditions, the as-developed colorimetric sensor displayed a wide linear range of 0.05-40 ng/mL with a detection limit of 3.52 pg/mL. Furthermore, this colorimetric sensor has been successfully applied to the detection of CEA in human serum samples. Therefore, the as-developed colorimetric sensor has broad application prospects in the field of medical diagnosis and portable detection.

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.

Polydopamine nanospheres with multiple quenching effect on TiO2/CdS:Mn for highly sensitive photoelectrochemical assay of tumor markers

A photoelectrochemical (PEC) immunosensing strategy based on the multiple quenching of polydopamine nanoparticles (PDA NPs) to Mn²⁺-doped CdS-modified TiO₂ nanoparticles (TiO₂/CdS:Mn) was designed for the highly sensitive detection of carcinoembryonic antigen (CEA). The uniform PDA NPs possessed good dispersibility, good biocompatibility, and abundant functional groups for biomolecule assembly. They also had unique photophysical properties, with light absorption spanning the visible to infrared light range. When the immune-recognition brought the PDA NPs close to the TiO₂/CdS:Mn interface, the PDA NPs competed with TiO₂/CdS:Mn to absorb light, consumed photoelectrons generated in the TiO₂/CdS:Mn, and hindered the access of electron donors to photoactive materials. The contribution from these aspects thus led to a significant decrease in photocurrent. Benefiting from the multiple quenching mechanism, the PEC immunosensor showed high sensitivity for CEA detection. Under optimal conditions, a low detection limit of 0.02 pg/mL and a wide linear relationship from 0.1 pg/mL to 100 ng/mL were obtained. The immunoassay showed good reproducibility and stability, and good selectivity and high accuracy in serum sample analysis. In this regard, PEC immunosensors may have great application potential for screening tumor markers and the prevention and monitoring of serious diseases.

A novel sandwich-type SERS immunosensor for selective and sensitive carcinoembryonic antigen (CEA) detection

Monitoring the malignant tumors via cancer biomarkers is very significant process. Nonetheless, the practical clinical applications need selective and sensitive analytical methods/techniques. In this study, a novel sandwich type immunosensor based on surface-enhanced raman scattering (SERS) was presented including 4-mercaptobenzoic acid labeled MoS₂ nanoflowers@Au nanoparticles (MoS₂ NFs@Au NPs/ MBA) as CEASERS tag and Fe₃O₄@Au nanoparticles functionalized delaminated Ti₃C₂T_x MXene (Fe₃O₄ NPs@Au NPs/d-Ti₃C₂T_X MXene) as SERS magnetic supporting substrate for carcinoembryonic antigen (CEA) detection. Especially, the determination of single molecule by using SERS method enables early diagnosis of major diseases. In addition, this technique can be utilized for multiplex analyzes owing to narrow well-resolved peaks. The prepared CEASERS tag and SERS magnetic supporting substrate were characterized by scanning electron microscope (SEM), x-ray diffraction (XRD) method, x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and fourier transform infrared spectroscopy (FTIR). A linearity of 0.0001-100.0 ng mL^-1 was observed with high sensitivity. Finally, sandwich type immunosensor demonstrated good selectivity and stability for target CEA recognition in plasma sample.

Antigen down format photoelectrochemical analysis supported by fullerene functionalized Sn3O4

Herein, a smart competitive-type photoelectrochemical (PEC) sensor based on an antigen-down (Ag-down) format for procalcitonin (PCT) detection is proposed. A fullerene sensitized flower-like Sn₃O₄ nano-structure is used as the photoactive platform, and FeS₂ is labeled on the secondary antibody as a signal adjusting element. The sensor exhibits excellent sensitivity and great stability.

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

We report here CdS quantum-dots (QDs)-decorated V₂O₅ nanosheets as high-performance and chemically etchable photoelectric active materials for constructing a photoelectrochemical (PEC) immunoassay platform. CdS QDs-decorated V₂O₅ nanosheets as new photoelectric materials can show superior photocurrent to V₂O₅ nanosheets and CdS QDs under visible-light irradiation because of the promoted photogenerated electron-hole separation and the increased visible-light absorption. V₂O₅ nanosheets can be etched by ascorbic acid (AA) because of the reduction of V₂O₅ to V⁴⁺, and the photocurrent of CdS/V₂O₅-nanocomposite-modified indium tin oxide electrode decreases significantly after being etched by AA. Inspired by this phenomenon, a PEC immunoassay platform is constructed for carcinoembryonic antigen (CEA) detection by using CdS/V₂O₅ nanocomposite as the photoelectric material and AA-encapsulated liposome immunonanocapsules as labels. The linear detection range for detecting CEA is from 0.5 pg mL^-1 to 1 ng mL^-1, with a limit of detection of 0.1 pg mL^-1. The proposed method also shows good selectivity, excellent reproducibility, and satisfactory recovery in detection of CEA in human serum samples. We believe that this work will lay the foundation for the future development of V₂O₅-based materials for PEC analysis, and also provide a reasonable design and implementation for the development of PEC immunoassay.

In situ amplified QCM immunoassay for carcinoembryonic antigen with colorectal cancer using horseradish peroxidase nanospheres and enzymatic biocatalytic precipitation

An innovative quartz crystal microbalance immunoassay was designed for detection of carcinoembryonic antigen using horseradish peroxidasenanoparticle as the enhancer, accompanying enzymatic biocatalytic precipitation toward 4-chloro-1-naphthol.