Photothermal biosensing integrated with microfluidic paper-based analytical device for sensitive quantification of sarcosine.

This article presents the development of a photothermal biosensing integrated with microfluidic paper-based analytical device (PT-µPAD) as a quantitative biosensor method for monitoring sarcosine in human control urine, plasma, and serum samples. The device utilizes gold nanoparticles (AuNPs) as both a peroxidase-like nanozyme and a photothermal substrate to enable sarcosine detection. In our PT-µPAD, hydrogen peroxide (H2O2) is generated through the oxidation of sarcosine by a sarcosine oxidase (SOx) enzyme. Subsequently, the H2O2 flows through the paper microchannels to the detection zone, where it etches the pre-deposited AuNPs, inducing a temperature change upon exposure by a 532 nm laser. The temperature variation is then measured using a portable and inexpensive infrared thermometer. Under optimized conditions, we obtained a linear range between 10.0 and 40.0 nmol L-1 (R2 = 0.9954) and a detection limit (LOD) of 32.0 pmol L-1. These values fall within the clinical range for sarcosine monitoring in prostate cancer diagnostics in humans. Moreover, our approach exhibits high selectivity without interfering effects. Recovery studies in various human control samples demonstrated a range of 99.05-102.11 % with the highest RSD of 2.25 %. The PT-µPAD was further validated for sarcosine determination in human control urine and compared with a commercial ELISA assay, revealing no significant difference between these two methods at a 95 % confidence level. Overall, our proposed sarcosine biosensor is well-suited for prostate cancer monitoring, given its affordability, sensitivity, and user-friendliness, even for unskilled individuals. Moreover, this strategy has promising prospects for broader applications, potentially detecting various biomarkers as a point-of-care (POC) diagnostic tool.

Greener analytical method for the determination of copper(II) in wastewater by micro flow system with optical sensor.

Greener analytical method using micro flow system for the determination of Cu(II) in wastewater samples was designed and investigated. The micro flow system consisted of a planar glass chip with poly(dimethylsiloxane) (PDMS) top plate and fixed with fiber optic probe as optical sensor for monitoring of Cu(II) that reacted with 2-carboxy-2'-hydroxy-5'-sulfoformazyl benzene (zincon) on the chip at 605nm. This design gave a satisfied sensitivity with a linear calibration graph over the range of 0.1-3.0mugmL(-1) of Cu(II) and correlation coefficient 0.9991. The percentage relative standard deviation was 2.5 for 10-replicate measurements and the limit of detection (LOD) was 0.1mugmL(-1). This system has been successfully applied to the determination of Cu(II) in wastewaters from electroplating industry with less reagents and samples consumption and diminutive waste generation.

Ultrasound-enhanced flow injection chemiluminescence for determination of hydrogen peroxide.

A novel ultrasonic flow injection chemiluminescence (FI-CL) manifold for determining hydrogen peroxide (H2O2) has been designed and evaluated. Chemiluminescence obtained from the luminol-H2O2-cobalt(II) reaction was enhanced by applying 120 W of ultrasound for a period of 4 s to the reaction coil in the FI-CL system and this enhancement was verified by comparison with an identical manifold without ultrasound. The system was developed for determining ultra-trace levels of H2O2 and a calibration curve was obtained with a linear portion over the range of 10-200 nmol L(-1) H2O2 (correlation coefficient 0.9945). The detection limit (3sigma) and the quantification limit (LOQ) were found to be 1 x 10(-9) and 3.3 x 10(-9) mol L(-1) respectively and the relative standard deviation was 1.37% for 2 x 10(-7) mol L(-1) H2O2 (n = 10). The method was applied to the determination of trace amounts of H2O2 in purified water and natural water samples without any special pre-treatments.

The development of sequential injection analysis coupled with lab-on-valve for copper determination.

A sequential injection analysis (SIA) using lab-on-valve with air segmentation and spectrophotometric detection was designed for copper(II) determination. It is based on the reaction of copper(II) and 2-carboxy-2'-hydroxy-5'-sulfoformazyl benzene (Zincon) in a weak alkaline solution between the air zones. Beer's Law was obeyed over the range of 0.1-2.0mgL(-1) copper(II) with a correlation coefficient 0.9985 and a slope of 0.2893 absorbance unit/mgL(-1). The relative standard deviation was 2.0% for a series of 10 measurements of 0.5mgL(-1) copper(II) solution. The detection limit (3 S/N) and the limit of quantification (LOQ) were 0.05 and 0.17mgL(-1) respectively. This method has been successfully applied to determination of copper(II) in wastewater with a sample throughput of 120h(-1). The method is superior to the batchwise method in that it provides fully automation, rapidity, less reagents and sample consumption with little waste generation.