Integrated hand-held electrochemical sensor for multicomponent detection in urine

Highlights

• A hand-held and three-electrode-integrated electrochemical device was produced.

• Operation is simplified to the utmost and a single hand can complete all steps.

• Novel sensing strategy was proposed to fulfill multicomponent analysis using a single WE.

• Impact of sample pH on detection was diminished by introducing pH values for calibration.

• The proposed sensor features simple fabrication and is free from any modification.

Abstract

Electrochemical sensors have shown great advantage and application potential in point-of-care testing (POCT) related scenarios. However, some fatal problems plague its widespread utilization, which include the susceptibility of sensors to interference in real samples (e.g. pH), the contradiction between the limited objects detectable for most sensors and the requirement of multi-target analysis in most cases, and the complicated procedures in sensor preparation as well as in routine use. This paper contributed a tip-like electrochemical sensor prototype. By integrated with a commercial pipettor, it fulfilled semi-automatic assay procedure of sampling, detection and rinsing, thus saving operational time and manual work. The tip sensor owns the property of simple fabrication and is free from any modification of extra bio/chem materials. Moreover, built on multiple electrochemical signal outputs including open circuit potential, peak current and potential of specific electrochemical reaction, this work established a novel multi-component sensing strategy, wherein detection of uric acid (UA), urea and pH in urine samples was realized by using one single working electrode. The detection range for the above targets is 5.0~600 μM for UA, 4.0~8.0 for pH and 0.5~7.0 mM for urea with the detection limits (S/N = 3) of 0.05 μM for UA and 5.4 μM for urea, and the sensitivity of pH assay is 73 mV/pH. Notably, as variation of sample pH has impact on electrochemical analysis, the pH-related parameter was introduced for calibration to diminish such interference. The developed tip sensor and the novel sensing strategy may open a new window for electrochemical technology and broaden its application in POCT.

Introduction

Point-of-care testing (POCT) is an analytical method performed at the sampling site by using portable instruments and supporting reagents to quickly obtain test results (Bhattacharjee et al., 2017; Guo, 2017). The most common analytical techniques serving POCT include colorimetry, fluorometry, electrochemical sensing, etc (Gubala et al., 2012; Tu et al., 2020). Among others, electrochemical sensing strategy features several advantages like high sensitivity, easy operation, and no need of complex optical devices (Guo, 2016, 2017). Some healthcare giant companies, e.g., Abbott, provide a variety of diagnostic instruments and products based on electrochemical strategy for analysis of biomarkers in human body fluids. Urine as a hands-down sample is frequently used in clinical and domestic tests, and some components in urine such as uric acid (UA), urea, creatinine and hydrogen ion, are important biomarkers indicating kidney disease, urarthritis, electrolyte disturbance, etc (Bernal-Reyes et al., 2020; Garcia-Trabanino et al., 2015). In recent years, electrochemical sensing strategy for analyzing the above markers in urine as well as in serum has scored some achievements (Pundir et al. 2019a, 2019b; Wang et al., 2020).

However, the pH value of urine is more labile (from 4.5 to 8.0) against that in serum and subcutaneous interstitial fluid, which remarkably affects electrochemical signals (Liu et al., 2019; Zhu et al., 2020). Therefore, accurate analysis of urine sample is difficult, unless urine pH is pre-determined and adjusted to the required condition, which undoubtedly increases complexity of detection process. The other issue is that current mainstream concepts of evidence-based medicine and individualized diagnosis emphasize cross-integration analysis of multiple medical indicators. However, almost all the electrochemical strategies reported focus on single substance detection (e.g. UA or urea) (Huang et al., 2017; Jakhar and Pundir, 2018; Liu et al., 2018; Song et al., 2014; Wang et al., 2020), and simultaneous analysis of two or more substances is rarely possible by using one sensor element. Even though sensor array system can realize multi-component assay, the complicated fabrication and modification procedure inevitably increases technical difficulty and expense, consequently hindering its widespread use (Atighilorestani and Brolo, 2017; Mishra et al., 2020). Obviously, there is a great demand for multiplexed quantification serving POCT with low technical threshold.

Additionally, modification of sensing element is common in most reported sensor system, which costs much and limits large-scale production (Abdel-Aziz et al., 2020; Findik et al., 2021; Yang et al., 2017). Besides, “sample in and result out” model is highly required from the customer's perspective in POCT utilization. However, the current electrochemical sensing development is far behind this goal. For example, the typical three-electrode system needs not only several milliliter volumes of sample, but also involves tedious operation (Zhang et al., 2020). Even though some emerging techniques such as microfluidic chip have been introduced to realize lab-on-a-chip concept, but chip fabrication still costs a lot and extra accessories like pumps impair practicability and portability (Nikolaev et al., 2020; Rodrigues et al., 2020).

In this work, we concentrate on facilitating urine sample analysis based on electrochemical strategy from the instrumental and methodological aspects. A novel POCT device for multi-component quantification of urine sample was designed, and the accompanying analytical methods were developed. The POCT device is a tip-like tubular sensor integrated with three electrodes. With the assistance of a pipettor, the tubular sensor can realize semi-automatic procedure including sampling, determination, washing and regeneration, and thus simplify manual work to the utmost. As for the analytical methods, detection of three analytes (UA, pH and urea) were achieved using one working electrode. Specifically, the oxidation current and potential of UA were utilized as the output signals for assaying UA and pH value, respectively. Urea measurement was based on the open circuit potential (OCP) shift before and after addition of urease in sample. Finally, both the POCT device and the newly developed methods were verified by analyzing real samples.