Advanced trap lateral flow immunoassay sensor for the detection of cortisol in human bodily fluids.

Paper-based biosensors based on lateral flow immunoassay (LFI) are promising candidates for POC diagnosis because of their ease of use and rapid target detection. However, the low sensitivity of LFI limits its application, and signal amplification has been used in numerous studies to increase its sensitivity. We developed an advanced trap LFI (α-trapLFI), a simple-to-use sensor, with an additional step for signal amplification. Here, signal amplification is automatically implemented following delayed release of enhancement solution induced by water-soluble polyvinyl alcohol tape. As the polyvinyl alcohol tape is exposed to water, its polymer structure is perturbed (within 5 min), allowing ions to pass through. This new sensor was designed to have a short time delay between the flow of solutions used for the immunoassay and signal amplification. The α-trapLFI was subsequently used to detect cortisol with high sensitivity (9.1 pg∙mL-1) over a broad detection range (0.01-1000 ng∙mL-1) in bodily fluids. Furthermore, an excellent correlation was obtained by analyzing 20 human real saliva samples using this sensor and a conventional ELISA (R2 = 0.90). The new sensor will be helpful in detecting various small molecules for simple, rapid, and portable POC diagnosis of stress disorders.

Reactant/polymer hybrid films on p-n junction photodetectors for self-powered, non-invasive glucose biosensors.

The portability of electronic-based biosensors is limited because of the use of batteries and/or solutions containing reactants such as enzymes for assay, which limits the utility of such biosensors in point-of-care (POC) testing. In this study, we report on the development of a self-powered biosensor composed of only portable components: a reactant-containing poly (ethylene glycol) (PEG) film for the colorimetric assay, and a self-powered n-InGaZnO/p-Si photodetector. The PEG film containing enzymes and color-developing agents was formed on a glass slide by spin coating. The self-powered biosensor was fabricated by placing the hybrid film on the p-n junction photodetector, and applied in non-invasive glucose detection (salivary glucose). Injection of the target-containing solution dissolved the PEG that led to the release of enzymes and color-developing agents, resulting in a colorimetric assay. The colorimetric assay could attenuate the light reaching the photodetector, thus facilitating target concentration verification by measuring the photocurrent. Our self-powered biosensor has two main advantages: (i) all components of the biosensor are portable and (ii) dilution of target concentration is avoided as the reagents are in the PEG film. Therefore, the self-powered biosensor, without solution-phase components, could be highly beneficial for creating portable, sensitive biosensors for POC testing.

Advanced Colorimetric Paper Sensors Using Color Focusing Effect Based on Asymmetric Flow of Fluid.

Although paper-based colorimetric sensors utilizing enzymatic reactions are well suited for real-field diagnosis, their widespread use is hindered by signal blurring at the detection spot due to the action of capillary forces on the liquid and the corresponding membrane. In this study, we eliminated signal losses commonly observed during enzyme-mediated colorimetric sensing and achieved pattern-free quantitative analysis of glucose and uric acid by mixing enzymes and color-forming reagents with chitosan oligosaccharide lactate (COL), which resulted in perfectly focused colorimetric signals at the detection spot, using asymmetric flow induced by changing the flow rate of the COL-treated paper. The targets were calibrated with 0-500 mg/dL of glucose and 0-200 mg/dL of uric acid, and the limit of detection was calculated to be 0.6 and 0.03 mg/dL, respectively. In human urine, the correlation has a high response between the measured and spiked concentrations, and the stability of the enzyme mixture including COL increased by 41% for glucose oxidase mixture and 29% for uricase mixture, compared to the corresponding mixtures without COL. Thus, the color focusing and pattern-free sensor, which have the advantages of easy fabrication, easy handling, and high stability, should be applied to real-field diagnosis.

Self-Powered Biosensors Using Various Light Sources in Daily Life Environments: Integration of p-n Heterojunction Photodetectors and Colorimetric Reactions for Biomolecule Detection.

Electronic biosensors operating without power supply are high in demand owing to increasing interest in point-of-care (POC) coupled with portable and wearable electronic devices for smart healthcare services. Although self-powered electronic sensors have emerged with the promise of resolving the energy supply problems, achieving sufficient sensitivity to targets in real samples is highly challenging because of the matrix effect caused by electroactive species. In this study, we developed a self-powered biosensor platform by combining n-indium gallium zinc oxide (IGZO)/p-Si heterojunction photodetectors and physically separated colorimetric reactions. The self-powered biosensors were applied to glucose detection in real human samples using light sources from daily life environments such as fluorescent light and sunlight. The sensors showed high sensitivity and stability from 0.01 to 10 mg mL-1 of glucose in human saliva and urine without matrix effect from the electroactive species in real samples. In addition, a small change in glucose concentration in human serum was distinguishable with a resolution of 0.01 mg mL-1. Notably, these results were obtained using well-developed and widely used materials like Si and IGZO with simple deposition techniques. Moreover, this self-powered biosensing platform can be universally applied for the detection of all biomolecules being detected by colorimetric assays. To the best of our knowledge, this is the first report on such self-powered biosensors, which could be a promising candidate for future POC biosensors integrated with portable and wearable electronic devices.