Development of a Novel Benzimidazole-Based Probe and Portable Fluorimeter for the Detection of Cysteine in Human Urine

A self-cascade system based on Ag nanoparticle/single-walled carbon nanotube nanocomposites as an enzyme mimic for ultrasensitive detection of L-cysteine

L-Cysteine, widely used in medicine and the food industry, is of great essentiality to organisms and the food quality. Given that current detection approaches require exacting lab conditions and tedious sample treatment, there is a pressing demand for developing a method that possesses advantages of user friendliness, prominent performance, and cost-effectiveness. Herein, a self-cascade system was developed for the fluorescence detection of L-cysteine based on the ingenious performance of Ag nanoparticle/single-walled carbon nanotube nanocomposites (AgNP/SWCNTs) and DNA-templated Ag nanoclusters (DNA-AgNCs). The fluorescence of DNA-AgNCs could be quenched on account of the adsorption of DNA-AgNCs on AgNP/SWCNTs by π-π stacking. With the cooperation of Fe²⁺, AgNP/SWCNTs with oxidase and peroxidase-like activities could catalyze the oxidation of L-cysteine to produce cystine and hydrogen peroxide (H₂O₂) and then break the O-O bond of H₂O₂ to generate a hydroxyl radical (·OH), which could cleave the DNA strand into different sequence fragments which subsequently peeled off from the AgNP/SWCNTs, resulting in a "turn-on" fluorescence response. In this paper, AgNP/SWCNTs with multi-enzyme activities was synthesized enabling the reaction to proceed in just one step. The successful preliminary applications for the L-cysteine detection in pharmaceutical, juice beverage, and serum samples indicated that the developed method exhibited great potential in medical diagnosis, food monitoring, and the biochemical field, which also broadened the horizon for follow-up research.

A Flexible Optoelectronic Device for Continuous Cerebral Blood Flow Monitoring

Human cerebral oxygenation and hemodynamics can be estimated by cerebral oxygenation parameters. Functional near-infrared spectroscopy (fNIRS) can be used to measure the hemoglobin concentration index of brain tissue noninvasively and in real time. However, limited by cumbersome equipment, high price and uncomfortable wear, conventional fNIRS monitoring systems still cannot achieve continuous and long-term monitoring. In this work, a flexible and wearable long-term monitoring system is developed featured with cost efficiency, simple preparation and light weight (only 1.6 g), which consists of a pair of light-emitting diodes (LEDs) and a photodetector (PD). Triangular serpentine interconnectors are introduced to connect the functional elements, enabling the device to be stretched in multiple directions. The device can continuously work for 7 h and be subjected to 2000 cycles of bending loading, with less than 3% change in voltage value, 1.89% and 1.9% change in LED luminous power and 0.9% change in voltage value. Furthermore, the hand-gripping and breath-holding experiments show that the system can accurately measure the changes in hemoglobin concentration in accordance with the commercial device. The flexible fNIRS system presented here not only provides a simple preparation process but also offers new ideas for daily cerebral state monitoring and prolonged clinical monitoring.

Microfluidic Sliding Paper-Based Device for Point-of-Care Determination of Albumin-to-Creatine Ratio in Human Urine

A novel assay platform consisting of a microfluidic sliding double-track paper-based chip and a hand-held Raspberry Pi detection system is proposed for determining the albumin-to-creatine ratio (ACR) in human urine. It is a clinically important parameter and can be used for the early detection of related diseases, such as renal insufficiency. In the proposed method, the sliding layer of the microchip is applied and the sample diffuses through two parallel filtration channels to the reaction/detection areas of the microchip to complete the detection reaction, which is a simple method well suited for self-diagnosis of ACR index in human urine. The RGB (red, green, and blue) value intensity signals of the reaction complexes in these two reaction zones are analyzed by a Raspberry Pi computer to derive the ACR value (ALB and CRE concentrations). It is shown that the G + B value intensity signal is linearly related to the ALB and CRE concentrations with the correlation coefficients of R2 = 0.9919 and R2 = 0.9923, respectively. It is additionally shown that the ALB and CRE concentration results determined using the proposed method for 23 urine samples were collected from real suffering chronic kidney disease (CKD) patients are in fine agreement with those acquired operating a traditional high-reliability macroscale method. Overall, for point-of-care (POC) CKD diagnosis and monitoring in clinical applications, the results prove that the proposed method offers a convenient, real time, reliable, and low-spending solution for POC CKD diagnosis.