Utilization of self-powered electrochemical systems: Metallic nanoparticle synthesis and lactate detection

Highlights

• The self-powered electrochemical systems based on triboelectric nanogenerators as the power source have been successfully demonstrated.

• The novel application of self-powered electrochemical systems for the synthesis of size-controlled monometallic and bimetallic nanoparticles is validated.

• In addition, the lightweight and fully self-powered electrochemical sensing system empowers the populace to manage and self-monitor lactate concentration in sweat anytime and anywhere.

• The wearable self-powered sensing system requires mere seconds to generate adequate electricity before driving the electrochemical reaction to complete lactate detection.

Abstract

Since the introduction of the first expounded triboelectric nanogenerator (TENG) in 2012, the theoretical and practical aspects of the TENG have been researched as an alternative energy harvesting technology to convert mechanical energy into electricity efficiently. Numerous self-powered sensing systems have adopted the TENG as a power source to further explore its versatile applications toward different targets. In this study, we employed a TENG to replace a traditional power supply for synthesizing different metallic nanoparticles using an electrochemical approach. Carbon fibers were adopted as the conductive substrates to grow the metallic nanoparticles, where the size and density of the nanoparticles on carbon fibers can be controlled by the electric output of the TENG. Additionally, we demonstrated that the as-prepared carbon modified and integrated with the TENG to construct a wearable self-powered sensing system exhibited significant selectivity and sensitivity toward lactate detection. Furthermore, the design of the sensing unit was favorable regarding its adaptability and flexibility to fit human body shapes and postures. As demonstrated in this study, the as-prepared self-powered sensing system could detect the lactate concentration in human perspiration, which can be an ideal wearable device for end users who seek real-time monitoring of their physical condition. This study concludes with a proposal for noninvasive biosensors, which provide boundless potential for future cross-field applications.

Introduction

Recent trends in the aging population and the raised awareness of healthcare have given rise to increasing expenses in wearable sensing devices that target daily healthcare management and have further driven research in wearable sensing technology from a biological perspective [4], [5], [6]. With all the developments and advances achieved by investigations of wearable biosensor systems for health monitoring, continued attention has been paid by the scientific community and industry to explore the possibilities of biosensors in medical diagnostics [1], [2], [3]. To address such a demand, a variety of commercial wearable devices and system prototypes have been introduced, claiming the features of a real-time response and an alert to an individual's state of health for purposes of fitness management, chronic disorder monitoring, etc [7], [8], [9]. As an alternative to traditional invasive treatments, a wearable health monitoring system offers noninvasive approaches to detect vital signs with extensive targets ranging from hyperglycemia [10], hypertension [11], cholesterol control [12], and lactate management [13]. For practical concerns, an ideal wearable device should be compact, lightweight and highly sensitive to meet the demands of both portability and responsiveness, where the self-powered biosensor has unequaled advantages for this application.

A self-powered sensor is able to meet the dual requirements of a compact form factor and a sufficient power supply through the integration of a nanogenerator [14]. Using the concept of a self-powered system, electricity generation and other manners of applications are achieved through the collection of renewable energy based on thermoelectric [15], piezoelectric [16], photovoltaic [17] and triboelectric effects [18]. Among the devices built with an energy harvesting mechanism, a triboelectric nanogenerator (TENG) demonstrates superior output performance with a broad range of alternative and affordable outlay materials, showing its promising potential for versatile applications [19], [20], [21], [22]. A TENG can either be designed as a compact and portable power supply device [23], [24], [25]; or through surface modification [26], [27], [28] to function as a self-powered nanosensor. Furthermore, it has been a common approach to enhance the sensitivity of these self-powered sensing systems through the introduction of nanoparticles [29], [30], [31]. Nanoparticles are of great scientific interest as they bridge the gap between bulk materials and atomic or molecular structures [32]. For example, metallic nanoparticles have considerable applications in diverse fields such as electronics [33], biotechnology [34], cosmetics [35], coatings [36], and packaging [37]. In previous studies, bimetallic nanoparticles have shown superiority over monometallic nanoparticles in terms of catalytic activity [38], [39], [40]. In this study, we managed to directly grow monometallic and bimetallic nanoparticles on weavable, extra lightweight and highly electrically conductive carbon fibers through a TENG-based self-powered electrochemical system.

Breakthroughs in biosensors have contributed to biomedical diagnostics and healthcare management by means of the biochemical interaction between a sensor and an analyte with specificity [41], [42], [43], [44]. Lactate, a major metabolite in the anaerobic glycolytic pathway, can function in several biochemical reactions and serve as the critical factor under monitoring circumstances such as surgery, respiratory failure, sepsis and histogenic hypoxia and high concentration accumulation will cause lactic acidosis [45]. Traditional lactate sensing is disadvantageous because it lacks time efficiency and result accuracy and thereby requires the development of a new prototype lactate biosensor [46], [47], [48]. In addition, we demonstrated that the TENG-based self-powered electrochemical system introduced a noninvasive lactate biosensor by utilizing the integration of a TENG to provide an instant inspection without an external energy supply. The illustration is shown in Fig. 1. Fig. 1a demonstrates a close-up look at the carbon fibers with metallic nanoparticles and lactate oxidase, and Fig. 1b is the depiction of our TENG. The as-prepared device is shown to possess tremendous commercial potential in providing comfortable wearing experiences as well as accurate monitoring results for end users.