A microfluidic analyzer based on liquid waveguide capillary cells for the high-sensitivity determination of phosphate in seawater and its applications

• Published in: Analytica chimica acta 2024-11, Vol.1329, p.343155, Article 343155
• Main Authors: Zhao, Jincheng, Yang, Zeming, Tang, Dejing, Qin, Min, Zhou, Wen, Liu, Cong, Xu, Zhantang, Cheng, Yuanyue, Zhang, Xianqing, Li, Cai
• Format: Article
• Language: English
• Subjects: High-sensitivity; Lab-on-a-Chip; Liquid waveguide capillary cell; Phosphate; Seawater; Shipboard underway analysis
• ISSN: 0003-2670; 1873-4324; 1873-4324
• DOI: 10.1016/j.aca.2024.343155

Optical detection is frequently performed on microfluidic chips for colorimetric analysis. Integrating liquid waveguide capillaries with total internal reflection with the microfluidic chip requires less procedures, which is suitable in the optical detection of microfluidic systems and is a practical alternative to increase the optical path length in the colorimetric assay of microfluidic devices for higher sensitivities and lower detection limit. However, this alternative has not been applied to the connection of PMMA chips or the microfluidic devices for the detection of phosphate in seawater. Here, a lab-on-a-chip system integrating a microfluidic chip and an external liquid waveguide capillary cell was presented to detect the phosphate in seawater. The detachable total internal reflection capillary made of Teflon AF 2400 connected to the chip transports sample and transmits light, greatly reducing detection limit, eliminating the interference from stray light and widening the dynamic range of the system without specific surface treatment of the microchannel. By utilizing an internal 5-cm absorption cell and an external 20-cm liquid waveguide capillary cell, the system reaches detection limits of 59 nM and 8 nM, respectively, and can detect phosphate concentration from 0 to 23 μM. An online analyzer was developed based on the high-sensitivity system and was applied to shipboard underway analysis for two scientific cruises and to laboratory measurements for seawater samples from Xisha sea area. Correlation analyses between the shipboard and laboratory phosphate measurements and other physical and biochemical elements revealed the marine ecological characteristics of the corresponding areas, demonstrating the high-sensitivity of this method over slight variations and narrow ranges of phosphate and the ability to provide microfluidic systems for high spatiotemporal resolution phosphate determination a practical and cost-effective alternative. [Display omitted] •First application of liquid waveguide capillary cell (LWCC) in microfluidic devices for seawater phosphate.•LOD for the phosphate using an external 20-cm LWCC is 8 nM, over 7 times the LOD using the 5-cm cell inside the PMMA chip.•Applications and analyses demonstrated the high-sensitivity method over slight variations and narrow ranges of phosphate.•Proposed method provides microfluidic systems for high-resolution determination a practical and cost-effective alternative.