A concentration−dependent multicolor conversion strategy for ultrasensitive colorimetric immunoassay with the naked eye

Prostate-Specific Antigen as an Ultrasensitive Biomarker for Patients with Early Recurrent Prostate Cancer: How Low Shall We Go? A Systematic Review

Serum prostate-specific antigen (PSA) needs to be monitored with ultrasensitive PSA assays (uPSAs) for oncologists to be able to start salvage radiotherapy (SRT) while PSA is <0.5 µg/L for patients with prostate cancer (PCa) relapsing after a radical prostatectomy (RP). Our systematic review (SR) aimed to summarize uPSAs for patients with localized PCa. The SR was registered as InPLASY2023110084. We searched for studies on Google Scholar, PUBMED and reference lists of reviews and studies. We only included studies on uPSAs published in English and excluded studies of women, animals, sarcoidosis and reviews. Of the 115 included studies, 39 reported PSA assay methods and 76 reported clinical findings. Of 67,479 patients, 14,965 developed PSA recurrence (PSAR) and 2663 died. Extremely low PSA nadir and early developments of PSA separated PSAR-prone from non-PSAR-prone patients (cumulative p value 3.7 × 1012). RP patients with the lowest post-surgery PSA nadir and patients who had the lowest PSA at SRT had the fewest deaths. In conclusion, PSA for patients with localized PCa in the pre-PSAR phase of PCa is strongly associated with later PSAR and survival. A rising but still exceedingly low PSA at SRT predicts a good 5-year overall survival.

A multicolor biosensor for alkaline phosphatase activity detection based on the peroxidase activity of copper nanoclusters and etching of gold nanorods

A multicolor biosensor for ALP activity has been developed based on the peroxidase activity of copper nanoclusters and etching of gold nanorods.

Lateral Flow Immunoassay Coupled with Copper Enhancement for Rapid and Sensitive SARS-CoV-2 Nucleocapsid Protein Detection

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory coronavirus 2 (SARS-CoV-2) is still raging all over the world. Hence, the rapid and sensitive screening of the suspected population is in high demand. The nucleocapsid protein (NP) of SARS-CoV-2 has been selected as an ideal marker for viral antigen detection. This study describes a lateral flow immunoassay (LFIA) based on colloidal gold nanoparticles for rapid NP antigen detection, in which sensitivity was improved through copper deposition-induced signal amplification. The detection sensitivity of the developed LFIA for NP antigen detection (using certified reference materials) under the optimized parameters was 0.01 μg/mL and was promoted by three orders of magnitude to 10 pg/mL after copper deposition signal amplification. The LFIA coupled with the copper enhancement technique has many merits such as low cost, high efficiency, and high sensitivity. It provides an effective approach to the rapid screening, diagnosis, and monitoring of the suspected population in the COVID-19 outbreak.

A DNA dendrimer amplified electrochemical immunosensing method for highly sensitive detection of prostate specific antigen

This work designed a DNA dendrimer for the loading of signal molecule and the construction of amplified electrochemical immunosensing method. The DNA dendrimer was self-assembled by the hybridization of one couple of complementary oligonucleotides (DNA and cDNA) that were covalently conjugated to three arms of a Y-shaped cross-linker, tris(2-maleimidoethyl)amine (TMEA) respectively. The immunosensor was prepared by coating chitosan on glassy carbon electrode to covalently immobilize the capture antibody with glutaraldehyde as a linker. After the target protein was captured on the immunosensor, cDNA-labeled secondary antibody was bound on the surface via a sandwiched immunoreaction to introduce the DNA dendrimer onto immunosensor for loading abundant methylene blue as signal molecule, which amplified greatly the amperometric signal for immunoassay. Using prostate specific antigen (PSA) as a model analyte, this proposed method showed a wide linear range from 1 pg mL^-1 to 10 ng mL^-1 along with a limit of detection down to 0.26 pg mL^-1. The designed strategy avoided complex synthesis of signal tags, and possessed excellent performance for analysis of practical samples, thus providing a new avenue for the development of signal amplification strategy and immunoassay methods.

Recent advances in visual detection for cancer biomarkers and infectious pathogens

It is an urgency to detect infectious pathogens or cancer biomarkers using rapid, simple, convenient and cost-effective methods in complex biological samples. Many existing approaches (traditional virus culture, ELISA or PCR) for the pathogen and biomarker assays face several challenges in the clinical applications that require lengthy time, sophisticated sample pre-treatment and expensive instruments. Due to the simple and rapid detection manner as well as no requirement of expensive equipment, many visual detection methods have been considered to resolve the aforementioned problems. Meanwhile, various new materials and colorimetric/fluorescent methods have been tried to construct new biosensors for infectious pathogens and biomarkers. However, the recent progress of these aspects is rarely reviewed, especially in terms of integration of new materials, microdevice and detection mechanism into the visual detection systems. Herein, we provide a broad field of view to discuss the recent progress in the visual detection of infectious pathogens and cancer biomarkers along with the detection mechanism, new materials, novel detection methods, special targets as well as multi-functional microdevices and systems. The novel visual approaches for the infectious pathogens and biomarkers, such as bioluminescence resonance energy transfer (BRET), metal-induced metallization and clustered regularly interspaced short palindromic repeats (CRISPR)-based biosensors, are discussed. Additionally, recent advancements in visual assays utilizing various new materials for proteins, nucleic acids, viruses, exosomes and small molecules are comprehensively reviewed. Future perspectives on the visual sensing systems for infectious pathogens and cancers are also proposed.

A simple thermometer-based photothermometric assay for alkaline phosphatase activity based on target-induced nanoprobe generation

Alkaline phosphatase (ALP)-induced in situ generation of Prussian blue nanoparticles for photothermometric ALP detection.

Colorimetric switchable linker-based bioassay for ultrasensitive detection of prostate-specific antigen as a cancer biomarker

The use of colorimetric bioassays for protein detection is one of the most interesting diagnostic approaches, but their relatively poor detection limits have been a critical issue. In this study, we developed an efficient colorimetric bioassay based on switchable linkers (SLs) for the detection of prostate-specific antigen (PSA), which is one of the most widely used protein biomarkers for the diagnosis of prostate and breast cancers. SLs can cross-link gold nanoparticles (AuNPs) to generate large-scale aggregates and thereby induce precipitation to achieve visual signal amplification. In addition, when SLs are occupied by target proteins (referred to as 'switch-off'), highly sensitive detection is enabled. To maximize sensitivity, we adjusted the total surface area of AuNPs by controlling their concentration. As a result, PSA was detected at an ultralow concentration of 100 fg mL-1. This SL-based assay is shown to be simple, easy to handle and visualize, and highly sensitive. Therefore, in addition to PSA, the proposed SL-based assay could be used to detect other protein biomarkers.

A Colorimetric Immunoassay Based on Coordination Polymer Composite for the Detection of Carcinoembryonic Antigen

Coordination polymers (CPs) as fascinating materials have been explored in a number of fields due to their diverse properties. In this work, we demonstrate the feasibility of CPs in the facile fabrication of multifunctional composites for establishing an immunoassay. To this end, a zinc(II)-based CP (ZnCP) with adenine as a bridge ligand was employed to integrate with alkaline phosphatase (ALP) and anticarcinoembryonic antigen (anti-CEA) antibody, which produces ALP/anti-CEA@ZnCPs. Benefiting from the adaptive inclusion property of ZnCPs, the integrated ALP and anti-CEA can maintain their original catalytic activity and capture ability to target antigen, respectively. This allows the ALP/anti-CEA@ZnCPs to be a detection antibody for performing an immunoassay. Meanwhile, ZnCP as a host can effectively protect the loaded ALP and anti-CEA against harsh environments. On this basis, by using iron(II)-phenanthroline complex as a signal amplifier, a colorimetric immunoassay for CEA detection was developed, and a low detection limit of 21.1 pg/mL has been achieved. This immunoassay was successfully applied to determine CEA levels in serum samples with good recovery and precision. We believe that this study can not only provide a new method for CEA detection but also open up a new way for the rational design and fabrication of multifunctional composites.

Colorimetric immunosensor for determination of prostate specific antigen using surface plasmon resonance band of colloidal triangular shape gold nanoparticles

In this work, we demonstrated the development of a colorimetric immunosensor using surface plasmon resonance band of gold nanoparticles for the detection of prostate specific antigen (PSA). To develop this biosensing tool, triangular gold nanoparticles (AuNPs) were synthesized using Tween-20 as a nonionic surfactant and then, conjugated with PSA capture antibody (Ab₁-AuNPs). When exposed to Ab₁-AuNPs, PSA antigens were found to be successfully captured by nanosystem (PSA)-Ab₁-AuNPs. Next, (PSA)-Ab₁-AuNPs were incubated with second PSA antibody (2)-decorated magnetite (Fe₃O₄-Ab₂) and separated by an external magnetic force to leave Ab₁-AuNPs in the supernatant solution to be directly analyzed using UV-Vis spectroscopy. It was found that the absorption intensity was directly proportional to the PSA concentration. As a result, the linear range for PSA detection was found to be 0.01-20 ng mL^-1 with a detection limit of 0.009 ng mL^-1. Because of significant stability of the prepared Ab₁-AuNPs and excellent selectivity to the PSA antigen, this simple and sensitive sensing system is proposed to be potentially effective in the fast and real-time analysis of clinical samples from prostate cancer patients. We believe that the simple platform of this immunosensor to be useful in the development of future point-of-care sensing tools, working on the quantification of biomarkers in a drop of blood.

Colorimetric Immunosensor Based on Au@g-C3N4-Doped Spongelike 3D Network Cellulose Hydrogels for Detecting α-Fetoprotein

A colorimetric immunoassay is a powerful tool for detecting tumor markers, with outstanding advantages of visualization and convenience. This study designed a colorimetric immunoassay using the antibody/antigen to control the catalytic activity to be "switched on/off". This system, where Au NPs (18.5 ± 3.9 nm) were loaded on the g-C₃N₄ nanosheets that were fixed in a three-dimensional porous cellulose hydrogel, was used as a binding site for the antibody/antigen. After being incubated with an antibody of a cancer marker, the turned-off catalytic sites on Au NPs in Au@g-C₃N₄/microcrystalline cellulose hydrogels would not be "turned on" until the corresponding antigen was added. The number of the recovered Au active sites was related to the amount of the antigen added. The Fourier transform infrared and X-ray photoelectron spectroscopy measurements did not detect the existence of Au-S bonds. Catalyzed by the turned-on Au NPs, 4-nitrophenol was reduced to 4-aminophenol accompanied by a color fading. The color and the absorption spectrum changes in the process were used as the colorimetric quantitative basis for immunoassays. The colorimetric immunoassay showed a linear relationship with the liver cancer marker (α-fetoprotein, AFP) in the range of 0.1-10 000 ng/mL with the detection limit of 0.46 ng/mL. In addition, 4-nitrophenol had a significant color fading when the AFP concentration exceeded the healthy human threshold. The clinical patient's serum test results obtained from the developed colorimetric immunosensor were consistent with those obtained from the commercial enzyme-linked immunosorbent assay. Furthermore, the immunosensor exhibited a good selectivity, repeatability, and stability, which demonstrated its potential for practical diagnostic application.

Paper-based fluorometric immunodevice with quantum-dot labeled antibodies for simultaneous detection of carcinoembryonic antigen and prostate specific antigen

A method is described for simultaneous fluorometric determination of the biomarkers carcinoembryonic antigen (CEA) and prostate specific antigen (PSA) on the same zone of a paper-based immunodevice. Two kinds of CdTe quantum dots, with respective emission peaks at 525 nm and 605 nm under a single excitation wavelength of 272 nm, were used to label the antibodies against CEA and PSA. Then the capture antibodies of CEA and PSA were immobilized on the same zone of the paper-based device. With the difference of the colors of the quantum dot fluorescence (green and orange), CEA and PSA can be detected on the same zone of the paper-based device. By using of sandwich immunoassay format, CEA and PSA can be simultaneously detected in human serum samples with a linear response in the 1.0-40 ng·mL^-1 concentration range for both. The recovery rates of the serum sample were in the range of 95-105%. The method has the potential of being applied to the simultaneous determination of various other kinds of substances on a single multichannel paper-based chip. Graphical abstract Schematic presentation of the simultaneous fluorometric detection of two cancer biomarkers on the same zone of the paper-based immunodevice is provided. Two kinds of CdTe quantum dots with different emission peaks under the same excitation wavelength are labeled on different detection antibodies.

A high-resolution colorimetric immunoassay platform realized by coupling enzymatic multicolor generation with smartphone readout

A high-resolution colorimetric immunoassay platform is developed based on dual enzyme-catalyzed multicolor generation and smartphone-assisted signal readout.