An ultrasensitive squamous cell carcinoma antigen biosensing platform utilizing double-antibody single-channel amplification strategy

β-Cyclodextrin-functionalized Ti3C2Tx MXene nanohybrids as innovative signal amplifiers for the electrochemical sandwich-like immunosensing of squamous cell carcinoma antigen

Herein, a simple and highly sensitive electrochemical sandwich-like immunosensor for the squamous cell carcinoma antigen (SCCA) was constructed using gold nanoparticle/graphene nanosheet (Au/GN) nanohybrids as a sensing platform and β-cyclodextrin/Ti₃C₂T_x MXenes (β-CD/Ti₃C₂T_x) as a signal amplifier. The good biocompatibility and large surface area as well as the high conductivity of Au/GN allow the platform to load primary antibodies (Ab₁) and facilitate electron transport. In the case of the β-CD/Ti₃C₂T_x nanohybrids, the β-CD molecule is dedicated to binding secondary antibodies (Ab₂) through host-guest interactions, thus inducing the formation of the sandwich-like structure Ab₂-β-CD/Ti₃C₂T_x/SCCA/Ab₁/Au/GN in the presence of SCCA. Interestingly, Cu²⁺ can be adsorbed and self-reduced on the surface of the sandwich-like structure to form Cu⁰ since Ti₃C₂T_x MXenes can exhibit superior adsorption and reduction capabilities towards Cu²⁺, and a prominent current signal of Cu⁰ can be observed via differential pulse voltammetry. Based on this principle, an innovative signal amplification strategy has been proposed for SCCA detection, which avoids the process of labeling the probe and the specific immobilization step of catalytic components on the surface of amplification markers. After the optimization of various conditions, a wide linear range from 0.05 pg mL^-1 to 20.0 ng mL^-1, coupled with a low detection limit of 0.01 pg mL^-1, was obtained for SCCA analysis. The proposed method for SCCA detection was also applied in real human serum samples and the observed results are satisfactory. This work opens up new pathways for constructing electrochemical sandwich-like immunosensors for SCCA and other targets.

Ultrasensitive sandwich-typed electrochemical immunoassay for detection of squamous cell carcinoma antigen based on highly branched PtCo nanocrystals and dendritic mesoporous SiO2@AuPt nanoparticles

Squamous cell carcinoma antigen (SCCA) is one of the common squamous cell carcinomas (SCC) in women, which usually works as a tumor biomarker for cervical cancer in diagnostic applications. Herein, bimetallic PtCo highly branched nanocrystals (PtCo BNCs) acted as electrode substrates to construct sandwich-typed electrochemical immunosensor for ultrasensitive detection of SCCA, by using dendritic mesoporous SiO₂@AuPt nanoparticles (DM-SiO₂@AuPt NPs) to adsorb electroactive thionine (Thi) as a signal label. The PtCo BNCs enlarged the loading of the primary antibody (Ab₁), showing effective improvement in conductivity and sensitivity. The DM-SiO₂ had abundant pores to incorporate more Thi, on which the decorated AuPt NPs created a great number of active sites to immobilize the secondary antibodies (Ab₂), thereby obviously amplifying the detection signals. The prepared sensor exhibited a broader linear range (0.001-120 ng mL^-1) and a lower detection limit (0.33 pg mL^-1, S/N = 3), combined with high reproducibility, a low relative standard deviation (below 2.5%) and acceptable recovery (from 98.5 to 110.0%) even in diluted human serum samples. This research provides a substantial platform for clinical diagnosis of SCCA in practice.

Nanostructure-Based Electrochemical Immunosensors as Diagnostic Tools

Electrochemical immunosensors are affinity-based biosensors characterized by several useful features such as specificity, miniaturizability, low cost and simplicity, making them very interesting for many applications in several scientific fields. One of the significant issues in the design of electrochemical immunosensors is to increase the system’s sensitivity. Different strategies have been developed, one of the most common is the use of nanostructured materials as electrode materials, nanocarriers, electroactive or electrocatalytic nanotracers because of their abilities in signal amplification and biocompatibility. In this review, we will consider some of the most used nanostructures employed in the development of electrochemical immunosensors (e.g., metallic nanoparticles, graphene, carbon nanotubes) and many other still uncommon nanomaterials. Furthermore, their diagnostic applications in the last decade will be discussed, referring to two relevant issues of present-day: the detection of tumor markers and viruses.

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.

Dual-responsive electrochemical immunosensor for detection of insulin based on dual-functional zinc silicate spheres-palladium nanoparticles

In this study, described an electrochemical immunoassay for insulin that is based on the use of zinc silicate spheres loaded with palladium nanoparticles (Zn₂SiO₄-PdNPs) that act as dual-function labels. The Zn₂SiO₄-PdNPs display high electrocatalytic activity towards the reduction of H₂O₂ and high sensitivity in chronoamperometry. The Zn₂SiO₄-PdNPs decrease the electron transfer rate between the electrolyte and the surface of the electrode, which can increase the changed current and enhance the sensitivity of the immunosensor as detected by square wave voltammetry (SWV). Electrodeposited gold is used as the matrix material. The icosahedral gold nanocrystals are coated with the primary antibodies formed a 3D mode to against abundant of insulin. Under optimal conditions, the assay has a linear response in the 0.1pgmL^-1 to 50ngmL^-1 insulin concentration range, and the limit of detection of the SWV and CA methods are 0.25 fg mL^-1 and 80 fg mL^-1, respectively. Moreover, the immunosensor holds an outstanding analytical performance for the insulin detection and has promising potential in clinical diagnosis.

Sulfur-Doped Graphene-Based Immunological Biosensing Platform for Multianalysis of Cancer Biomarkers

The accurate tumor marker detection at an early stage can prevent people from getting cancer to a great extent. Herein, a novel tri-antibody dual-channel biosensing strategy is applied in multianalysis of carcino-embryonic antigen (CEA) and nuclear matrix protein 22 (NMP22). In this immunosensor fabrication process, graphene oxide/polyaniline nanostructures are used as matrix and mesoporous NKF-5-3 is used as labels. Two kinds of antigens can be obtained from the signals of neutral red and toluidine blue, respectively, which are modified on the labels. In this tri-antibody dual-channel biosensing platform, sulfur-doped graphene sheet is synthesized by click chemistry as the framework structure. Majority of the incubations are conducted in individual steps, which ensure the surface incubation more tightly. The detection limit of NMP22 and CEA are 25 and 30 fg/mL, respectively. The low detection limit and excellent stability can ascribe to the tri-antibody dual-channel strategy, which makes the sensor platform from surface to the space. The clinical urine sample analysis achieves a good performance. The urine-based test can avoid the secondary injury on hemophilia or ischemic patients, displaying a potential application in clinical diagnosis.

Novel electrochemical immunoassay for human IgG1 using metal sulfide quantum dot-doped bovine serum albumin microspheres on antibody-functionalized magnetic beads

A new magneto-controlled electrochemical immunosensing system was developed for the sensitive detection of low-abundance protein (IgG1 used in this case) with a sandwich-type assay format on monoclonal mouse anti-human F_ab-specific IgG1-functionalized magnetic bead. Metal sulfide (CdS) quantum dot-doped bovine serum albumin (QD-BSA) was synthesized and functionalized with monoclonal F_c-specific anti-human antibody. In the presence of IgG1, the immobilized antibody on magnetic bead was selective to capture the F_ab region of the analyte, followed to be sandwiched by the conjugated antibody onto QD-BSA. The subsequent anodic stripping voltammetric analysis of cadmium ion, released by acid from quantum dot, was conducted at an in situ prepared mercury film electrode. Under optimal conditions, the voltammetric current increased with the increasing of target IgG1 within a dynamic working range from 10 pg mL^-1 to 100 ng mL^-1. The limit of detection of this immunosensor was evaluated to 3.4 pg mL^-1 at 3s_blank criterion. The precision, selectivity and method accuracy were acceptable. Analysis of human serum samples revealed good accordance with the results obtained by commercial enzyme-linked immunosorbent assay method. Importantly, this concept offers promise for cost-effective analysis of low-abundance cancer biomarkers without the need of natural enzymes.

A novel sandwich-type immunosensor based on three-dimensional graphene–Au aerogels and quaternary chalcogenide nanocrystals for the detection of carcino embryonic antigen

Cu₂ZnSnS₄ nanocrystals were firstly used as electrocatalysts in H₂O₂ reduction for ultrasensitive detection of carcino embryonic antigen.

A Novel Controlled Release Immunosensor based on Benzimidazole Functionalized SiO2 and Cyclodextrin Functionalized Gold

A novel controlled release system-based sandwich-type immunosensor is fabricated to detect squamous cell carcinoma antigen (SCCA). The 1-methyl-1H-benzimidazole functionalized mesoporous SiO₂ (MBI-MS) is used to load methylene blue (MB). β-cyclodextrin functionalized gold (CD-Au) is introduced as the gatekeeper for encapsulating MB and capturing the adamantly functional detection antibody (ADA-Ab₂). And pH stimulus serves as the trigger system to control the MB release. After the load of MB, the CD-Au blocks the pores of the MBI-MS by the host-guest interaction in the neutral condition. However, when the pH is below 7.0, CD-Au is separated from the surface of MBI-MS owing to the protonation of the aromatic amines. The encapsulated MB is released from the pores of MBI-MS and detected by square wave voltammetry. The controlled release immunosensor shows a relatively wide linear range from 0.001 to 20 ng·mL⁻¹ with a low detection limit of 0.25 pg·mL⁻¹. The immunosensor also shows good reproducibility and selectivity, which endows it broad application prospect in clinical research.

A robust electrochemiluminescence immunoassay for carcinoembryonic antigen detection based on a microtiter plate as a bridge and Au@Pd nanorods as a peroxidase mimic

The common drawbacks of most traditional electrochemiluminescence (ECL) immunoassays are the strict storage conditions for the ECL electrode and the steric hindrance caused by bovine serum albumin and antigen.

Electrochemical immunosensors and their recent nanomaterial-based signal amplification strategies: a review

In recent years, tremendous advances have been made in biosensors based on nanoscale electrochemical immunosensors for use in the fields of agriculture, food safety, biomedicine, quality control, and environmental and industrial monitoring.

Combination of dynamic magnetophoretic separation and stationary magnetic trap for highly sensitive and selective detection of Salmonella typhimurium in complex matrix

Foodborne illnesses have always been a serious problem that threats public health, so it is necessary to develop a method that can detect the pathogens rapidly and sensitively. In this study, we designed a magnetic controlled microfluidic device which integrated the dynamic magnetophoretic separation and stationary magnetic trap together for sensitive and selective detection of Salmonella typhimurium (S. typhimurium). Coupled with immunomagnetic nanospheres (IMNs), this device could separate and enrich the target pathogens and realize the sensitive detection of target pathogens on chip. Based on the principle of sandwich immunoassays, the trapped target pathogens identified by streptavidin modified QDs (SA-QDs) were detected under an inverted fluorescence microscopy. A linear range was exhibited at the concentration from 1.0×10(4) to 1.0×10(6) colony-forming units/mL (CFU/mL), the limit of detection (LOD) was as low as 5.4×10(3) CFU/mL in milk (considering the sample volume, the absolute detection limit corresponded to 540C FU). Compared with the device with stationary magnetic trap alone, the integrated device enhanced anti-interference ability and increased detection sensitivity through dynamic magnetophoretic separation, and made the detection in complex samples more accurate. In addition, it had excellent specificity and good reproducibility. The developed system provides a rapid, sensitive and accurate approach to detect pathogens in practice samples.

Ultrasensitive immunoassay for CA125 detection using acid site compound as signal and enhancer

A novel sensitive electrochemical immunosensor was proposed for detection of CA125 based on ferrocenecarboxylic acid (FA), HCl-doped polyaniline (H-PANI) and chitosan hydrochloride (CS-HCl), which were used as substrate materials to generate signal and to enlarge specific surface area. The composite of these three materials (acid center compound, FA@H-PANI@CS-HCl) can be connected by hydrogen (H) in each molecule. Ag@Co3O4 nanosheets were used in the immunosensor to amplify the antibody capacity and to enhance the sensitivity of the immunoassay. This kind of sensor was novel, concise and it is the first time to be used in the detection of CA125. The biosensor exhibited low detection limit (0.25 pg/mL) and wide linear range (0.001-25 ng/mL). The stability, selectivity and reproducibility were acceptable. Serum sample analysis proved that the proposed sensor owned well precision and it might be used in potential clinic testing application in the future.