Heavy metals high-sensitive detection by laser-induced breakdown spectroscopy based on radial electroosmotic flow-driven enrichment

Direct analysis of heavy metal elements in liquid water using femtosecond laser-induced breakdown spectroscopy for high-sensitivity detection

Laser-induced breakdown spectroscopy (LIBS) is a rapidly evolving in-situ multi-element analysis technique that has significantly advanced the field of liquid analysis. This study employs a femtosecond laser for quantitative analysis of heavy metals in flowing liquids, exploring its detection sensitivity and accuracy. Femtosecond pulsed laser excitation of water in a dynamic environment generates plasma while effectively preventing liquid splashing. The flowing water column maintains a stable liquid surface, avoiding irregular laser focusing caused by surface fluctuations. Calibration curves for chromium (Cr), lead (Pb), and copper (Cu) were established under optimized conditions at different numbers of spectral accumulations (NSAs). The limit of detection for Cr, Pb, and Cu were determined to be 0.061, 0.045, and 0.023; 0.475, 0.341, and 0.221; and 0.040, 0.027, and 0.019 μg/mL, respectively, for NSAs of 10, 20, and 50. Additionally, the R2 values of the polynomial fits exceeded 0.99, underscoring the reliability of the experimental approach. This study provides valuable insights into optimizing the analytical performance of LIBS for heavy metal detection in aqueous solutions, making it a powerful tool for environmental monitoring and industrial applications.

Design and fabrication of superhydrophobic microstructured grooved substrates to suppress the coffee-ring effect and enhance the stability of Sr element detection in liquids using LIBS

A new technique has been developed to enhance the stability of laser-induced breakdown spectroscopy (LIBS) in the analysis of dry droplets by mitigating the coffee ring effect (CRE) on substrates with superhydrophobic microstructured grooves. The substrate was prepared from a laser-etched pure copper base, resembling the surface of a lotus leaf, creating a biomimetic superhydrophobic substrate. The superhydrophobic microstructured grooved substrate contained an array of dome-shaped cones with heights of approximately 140 μm and 100 μm, arranged in a periodic pattern of high-low-high. The superhydrophobic properties of the substrate not only evaporation-induced thermal capillary action but also initiated the Marangoni flow, which moves from the periphery to the center of the droplet as it evaporates. This flow mechanism effectively mitigated the CRE by transporting the analyte from the bottom edge of the droplet across its surface to the central peak. To assess how these superhydrophobic microstructured grooved substrates impede the formation of coffee rings, LIBS was deployed to analyze samples from both structured and unstructured grooved substrates. The results indicated that the relative standard deviation (RSD) of the spectral intensity for Sr I at 407.67 nm in substrates with a superhydrophobic microstructured groove edge length of 0.8 mm was 3.6%. In contrast, for the unstructured grooved substrate and a side length of 0.9 mm, the RSD was significantly higher at 25.4%. This research demonstrates that substrates with superhydrophobic microstructured grooves are capable of effectively mitigating the CRE. Additionally, the study examined how the dimensions of these grooves impact the plasma characteristics across two distinct configurations. Based on these observations, calibration curves for Sr were developed using substrates with groove side lengths of 0.6 mm and 0.8 mm. The performance of the superhydrophobic microstructured grooved substrate was satisfactory, exhibiting determination coefficients (R2) of 0.994 and 0.995 for the Sr element. The detection limits (LOD) were notably low at 0.16 μg mL-1 and 0.11 μg mL-1. The average relative standard deviations (ARSD) were 7.2% and 4.9%, respectively. These results demonstrate that the superhydrophobic microstructured grooved substrate effectively mitigates the CRE, thereby enhancing the detection sensitivity and prediction accuracy for heavy metals. This provides a robust reference for selecting platforms using LIBS technology in the pre-treatment process.

Advancements in the research of finger-actuated POCT chips

Microfluidic point-of-care testing (POCT) chips are used to enable the mixing and reaction of small sample volumes, facilitating target molecule detection. Traditional methods for actuating POCT chips rely on external pumps or power supplies, which are complex and non-portable. The development of finger-actuated chips has reduced operational difficulty and improved portability, promoting the development of POCT chips. This paper reviews the significance, developments, and potential applications of finger-actuated POCT chips. Three methods for controlling the flow accuracy of finger-actuated chips are summarized: direct push, indirect control, and sample injection control method, along with their respective advantages and disadvantages. Meanwhile, a comprehensive analysis of multi-fluid driving modes is provided, categorizing them into single-push multi-driving and multi-push multi-driving modes. Furthermore, recent research breakthroughs in finger-actuated chips are thoroughly summarized, and their structures, driving, and detection methods are discussed. Finally, this paper discusses the driving performance of finger-actuated chips, the suitability of detection scenarios, and the compatibility with existing detection technologies. It also provides prospects for the future development and application of finger-actuated POCT chips.