Vascular endothelial growth factor (VEGF) is a crucial signaling protein for the tumor growth and metastasis, which is also acted as the biomarkers for various diseases. In this research, we fabricate an aptamer-antibody sensor for point-of-care test of VEGF. Firstly, target VEGF is captured by antibody immobilized on the microplate, and then binds with aptamer to form the sandwich structure. Next, with the assist of glucose oxidase (GOx)-functionalized ssDNAs, hybridization chain reaction occurs using the aptamer as the primer. Thus, GOx are greatly gathered on the microplate, which catalyzes the oxidization of glucose, leading to the pH change. As a result, the detect limit at a signal-to-noise was estimated to be 0.5pg/mL of target by pH meter, and 1.6pg/mL of VEGF was able to be distinguished by naked eyes. Meanwhile, this method has been used assay VEGF in the serum with the satisfactory results.

With the increase in cancer risk, early immunodiagnosis is of great significance for timely therapy. In this work, a DNA-mediated immunosensor for the highly sensitive detection of prostate specific antigen (PSA) is proposed, which is mainly based on a portable personal glucose meter (PGM). Gold nanoparticles (AuNPs) functionalized with PSA detection antibodies and DNA primers are introduced. When the target of the PSA is present, rolling circle amplification (RCA) reactions on AuNPs are triggered and numerous repeated RCA products hybridize with the DNA-conjugated invertase; thus the signal of the PGM is generated and the PSA is quantified indirectly. With the use of a portable PGM, our method realizes a linear detection range of 0.003-50 ng mL-1, with a low detection limit of 0.1 pg mL-1, which is comparable to that of the traditional methods using expensive apparatus. Besides, the analysis of clinical human serum samples is performed to investigate its good practicability. This simple, low-cost, and miniaturized immunosensor is promising for the point-of-care testing of cancer markers.

A portable electrochemical immunosensing protocol was designed for the sensitive detection of a disease-related tumor biomarker (carcinoembryonic antigen, CEA, used in this case) on a pH meter using glucose oxidase (GOx)-encapsulated gold hollow microspheres (AuHMs) for signal amplification. The assay was carried out on a monoclonal anti-CEA capture antibody-coated microplate with a sandwich-type reaction mode. The GOx-entrapped AuHM was first synthesized using the reverse micelle method and then used as the signal-generation tag for the labeling of polyclonal anti-CEA detection antibody. Accompanying the formation of the sandwiched immunocomplexes, the loaded GOx molecules in the microsphere could catalyze glucose into gluconic acid and hydrogen peroxide. The as-produced gluconic acid changed the microenvironment of the detection solution, thus resulting in the shift of the pH value, which could be quantitatively determined on a portable pH meter. The use of gold hollow microspheres was expected to enhance the loaded amount of GOx for signal amplification. Two labeling protocols including GOx-labeled secondary antibody and GOx-AuHM-labeled secondary antibody were investigated for CEA detection, and improved analytical features were acquired with GOx-AuHM labeling. With the GOx-AuHM labeling strategy, the pH meter-based immunosensing device exhibited a good analytical performance for CEA detection within the dynamic linear range of 0.1-100 ng mL-1 at a detection limit of 0.062 ng mL-1. The strong attachment of anti-CEA antibodies to GOx-AuHM brought a good repeatability and intermediate precision down to 10%. Importantly, no significant differences at the 0.05 significance level were encountered in the analysis of 12 human serum specimens between the developed immunoassay and the commercialized electrochemiluminescent method for CEA determination.

Here we innovate a portable and quantitative immunochromatographic assay (ICA) with a personal glucose meter (PGM) as readout for the detection of Escherichia coli O157:H7 (E. coli O157:H7). The carboxyl group coated FeO nanoparticles (MNPs) were synthesized by a one pot method and used as carriers of invertase and monoclonal antibody against E. coli O157:H7. Initially, the invertase and antibody double functionalized MNPs (Invertase-MNPs-IgG) conjugates were prepared and used as label probe in this assay system. Before laminating onto the baking card, the absorbent pad was soaked in sucrose solution and desiccated. MNPs produced brown band at the detection zone of the ICA when acting as direct labels. As they were also coupled with invertase, the invertase catalyzed the hydrolysis of sucrose on the absorbent pad into glucose, which was detected by the PGM. To increase the sensitivity, antibody functionalized MNPs were used to enrich E. coli O157:H7 from sample solution. The innovative aspect of this approach lies in the visualization and quantification of E. coli O157:H7 through Invertase-MNPs-IgG and the detection of glucose concentration using PGM. Although the feasibility is demonstrated using E. coli O157:H7 as a model analyte, this approach can be easily developed to be a universal analysis system and applied to detection of a wide variety of foodborne pathogens and protein biomarkers. This study proposed a qualitative and quantitative analysis device for the clinic diagnostics and food safety analysis.

Non-glucose biomarker-DNA oxidative damage biomarker 8-hydroxy-2'-deoxyguanosine (8-OHdG) has been successfully detected using a smartphone-enabled glucose meter. Through a series of immune reactions and enzymatic reactions on a solid lateral flow platform, 8-OHdG concentration has been converted to a relative amount of glucose, and therefore can be detected by conventional glucose meter directly. The device was able to detect 8-OHdG concentrations in phosphate buffer saline as low as 1.73 ng mL with a dynamic range of 1-200 ng mL. Considering the inherent advantages of the personal glucose meter, the demonstration of this device, therefore, should provide new opportunities for the monitoring of a wide range of biomarkers and various target analytes in connection with different molecular recognition events.

There is considerable demand for sensitive, selective, and portable detection of disease-associated proteins, particularly in clinical practice and diagnostic applications. Portable devices are highly desired for detection of disease biomarkers in daily life due to the advantages of being simple, rapid, user-friendly, and low-cost. Herein we report an enzyme-encapsulated liposome-linked immunosorbent assay for sensitive detection of proteins using personal glucose meters (PGM) for portable quantitative readout. Liposomes encapsulating a large amount of amyloglucosidase or invertase are surface-coated with recognition elements such as aptamers or antibodies for target recognition. By translating molecular recognition signal into a large amount of glucose with the encapsulated enzyme, disease biomarkers such as thrombin or C-reactive protein (CRP) can be quantitatively detected by a PGM with a high detection limit of 1.8 or 0.30 nM, respectively. With the advantages of portability, ease of use, and low-cost, the method reported here has potential for portable and quantitative detection of various targets for different POC testing scenarios, such as rapid diagnosis in clinic offices, health monitoring at the bedside, and chemical/biochemical safety control in the field.