Pathogenic bacterial contamination is a major threat to safety, human health, and ecosystems. Herein, we report an advantageous single-step, wash-free, and real-time bacterial detection platform operating with a single antibody. Escherichia coli was detected as a model analyte. This technology is based on graphene oxide-coated microplates (GOMs) and photoluminescent bioprobes (PLBs). On the one hand, using nonradiative energy transfer, GOMs are conceived to deactivate the photoluminescence of those PLBs that are not experimenting immunoreactions via antibody-bacterial membrane affinity. On the other hand, those PLBs experimenting immunoreactions preserve their photoluminescence because of both (i) the distance between the complex (PLBs-bacteria) and GOMs and (ii) the low affinity between the same complex and GOMs. With an optimal analytical performance of ∼30 min, the resulting bacterial detection platform was demonstrated to be fast and highly sensitive, exhibiting a limit of detection of ∼2 CFU mL–1. Industrial real samples were also successfully analyzed in a widely used format that is amenable to high-throughput applications. Moreover, the proposed technology is highly transformative, as graphene oxide is able to quench different fluorophores, and other analytes can be detected by simply changing the specific antibody.
Bacterial vaginosis (BV) affects reproductive-age women and can lead to pelvic inflammatory disease, postpartum endometritis, and preterm labor/delivery and predisposes the infection of sexually transmitted diseases. Typically, BV diagnosis involves the analysis of vaginal swab samples via microscopy operated by highly skilled personnel. Hence, novel approaches for BV diagnosis are an existing need. In response, the first immunosensing platform targeting sialidase, a BV biomarker, is reported. The nanophotonic operational principle of this biosensing platform allows for a cheaper, faster, and simpler analysis when compared with an indirect enzyme-linked immunosorbent assay (ELISA). The clinical evaluation of such a nanotechnology is highlighted, where 162 vaginal swab samples were analyzed with high sensitivity and specificity (96.29%, respectively). The resulting nanoimmunosensing platform offers a resourceful approach to perform a timely BV diagnosis.
Serological tests are crucial in a pandemic scenario, since they are a valuable tool to spot those citizens with potential immunity, specific regions with herd immunity or particular at-risk populations, as well as acquired immunity after vaccination. Hence, high-throughput, fast, cost-effective, and straightforward technologies facilitating interrogation of COVID-19 seroconversion are an existing need. Herein, we developed an innovative assay for the determination of COVID-19 seroconversion. Fluorophore-labeled SARS-CoV-2 spike receptor-binding domain recombinant protein (F-RBD) was discovered to operate as a bioprobe that emits a strong fluorescence upon COVID-19 antibody detection; however, F-RBD fluorescence was deactivated by graphene oxide-decorated surfaces when COVID-19 antibodies are absent in the sample. With a cost of less than 0.5 USD per test (at laboratory scale), the biosensing system offers optimum results within 42 min. To demonstrate that this technology is technically sound in a relevant environment, 34 human serum samples were analyzed and clearly differentiated, requiring a tiny amount of serum (1 μL to be later diluted in saline buffer).
Immunoassays are, at present, an important tool for diagnostics, drug development, and environmental monitoring. However, most immunoassays involve procedures that require many elements for their development. We introduce a novel biosensing platform based on fluorescence quenching caused by graphene oxide (GO) for the detection of Human-IgG and Prostate-Specific Antigen (PSA). We employ a single antibody for the capture and detection processes, avoiding washing steps. FITC fluorophore was conjugated with antibodies for H-IgG detection, whereas quantum dots were conjugated with antibodies for PSA detection. The simple biosensing platform consists of covering a 96-well microplate (with a polystyrene bottom) with GO. The graphene oxide adhesion is possible by way of electrostatic interactions between the plate surface modified with amino groups (positively charged) and the graphene oxide (negatively charged). This proposal showed an excellent response for the detection of Human-IgG, with acceptable precision (from 0.27% to 5%). The limit of detection reached for H-IgG was 3.35 ng mL-1. In the same manner, for PSA detection, the limit of detection reached was 0.02 ng mL-1 and the precision range was from 0.7% to 15.2%. Furthermore, this biosensing platform was demonstrated to operate with real samples of human urine doped with different concentrations of prostate-specific antigen.
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