Flexible electrochemical uric acid and glucose biosensor

Highlights

• PtNPs anchored to pyrenebutanoic acid, succinimide ester (PBSE) graphene electrode.

• PtNPs and PBSE is utilized for electrocatalytic signal amplification.

• PtNPs at laser scribed graphene (LSG) leads to sensitivity uric acid detection.

• Highly sensitive glucose detection using glucose oxidase at LSG/PBSE/PtNPs.

• The LSG/PBSE/PtNPs can be used for electrochemical detection of biomolecules.

Abstract

Fully integrated uric acid (UA) and glucose biosensors were fabricated on polydimethylsiloxane/polyimide platform by facile one step laser scribed technique. The laser scribed graphene (LSG) on the thin polyimide film was functionalized using pyrenebutanoic acid, succinimide ester (PBSE) to improve the electrochemical activity of the biosensors. The LSG was further decorated with platinum nanoparticles (PtNPs) to promote the electrocatalytic activity towards the oxidation of UA. Glucose oxidase was immobilized on the PtNPs modified surface for selective detection of glucose. The fabricated biosensors were characterized via scanning electron microscopy (SEM), Energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), and electrochemical methods (cyclic voltammetry and amperometry measurements). Outstanding electrocatalytic activities toward oxidation of UA and glucose were demonstrated. A wide detection range of 5 µM to 480 µM UA with a high sensitivity of 156.56 µA/mMcm² and a calculated detection limit (LOD) of 0.018 μM (S/N = 3) were achieved for the UA biosensor. The glucose biosensor exhibited a detection range of 5 µM to 3200 µM with a sensitivity of 12.64 µA/mMcm² and an LOD of 2.57 µM (S/N = 3). These integrated biosensors offer great promise for potential applications in wearable UA and glucose sensing due to their good sensitivity, selectivity, and stability properties.

Introduction

Common metabolites (glucose, lactate, uric acid, etc.) and electrolytes (chlorine, sodium, etc.) are detected by wearable devices for non-intrusive, continuous, and noninvasive monitoring [1], [2], [3], [4]. Uric acid (UA) has garnered attention as an endogenous biomarker for wound healing assessment [5], [6]. In recent years, many efforts have demonstrated non-healing wounds have elevated levels of UA, where the UA can diffuse into the sweat glands and tissues present in the wound proximity [7], [8]. Moreover, high glucose levels have been shown to weaken the bactericidal ability of white blood cells, thereby causing bacteria growth, slow healing, and infection at the wound site [9], [10]. Individuals who experience poor wound healing associated with diabetes also encounter other complications, such as heart disease, kidney disease, and eye problems, etc. [11], [12], [13], [14], [15]. Although the detection of glucose is widely investigated [2], [16], [17], [18], [19], the assessment of both uric acid and glucose level are rare [20], [21]. Flexible and stretchable platform can be realized through several complex clean room techniques including chemical vapor deposition, photolithography, dry etching, and film transfer [2], [22], [23], [24]. Recently, laser scribed graphene (LSG) has attracted much attention due to its ease of fabrication and printing scalability on flexible and stretchable platform. LSG is a straightforward fabrication procedure, where CO₂ laser burns a polyimide film (PI) or Kapton tape to create a three-dimensional (3D) graphene pattern. In the patterned areas, sp³-carbon atoms are transformed to sp²-carbon atoms via the photothermal process. However, applying LSG in the fabrication of biosensors is challenging due to its poor mechanical stability, and electrical and chemical properties. Since LSG flakes can easily shed from the burnt surface, a few approaches have been proposed for modifying the LSG. To increase conductivity, Ye et al. prepared an LSG film with metal doping of the PI precursor [25]. Another group improved electrochemical properties by doping the PI film with boron [26]. To increase mechanical stability and conductivity, Zahed et al. sprayed coated PEDOT: PSS on the fabricated LSG [27]. To increase mechanical stability and conductivity, Park et al. sprayed coated PEDOT: PSS on the fabricated LSG [28]. Yoon et al. modified LSG using acetic acid solution to introduce oxygen functional groups in the LSG film leading to improved electrochemical activity [19]. Functional groups have been demonstrated to improve the anchoring sites for the decoration of nanoparticles and immobilization of enzyme [28], [29]. The functionalization of LSG further enhances the interaction between LSG and loading materials, which modulates the tethering of nanomaterials and biomolecules. Due to the outstanding chemical properties of carboxylic groups-containing materials, COOH-substituted LSG is expected to have enhanced functionalization efficiency compared to a pristine LSG and exhibit a promising tendency to bind nanomaterials and biological materials without perturbing original structure of carbon-based materials [30], [31].

In this study, a fully integrated biosensor system was fabricated on polyimide platform via a one-step laser scribed technique. LSG flakes can easily detach from the substrate surface upon shedding and frequent bending, the shedding may further decrease the electrochemical properties of the LSG based biosensor. Here, the formed 3D graphene was functionalized using pyrenebutanoic acid, succinimide ester (PBSE) crosslinker to hold the LSG flakes intact on the PI surface and prevent the shedding of the LSG flakes and to improve the electrochemical activity of the LSG film. Since UA can easily be oxidized at common nonenzymatic biosensor, the LSG film was decorated with platinum nanoparticles (PtNPs) due to its outstanding catalytic activity towards biomolecules [32], [33]. The biosensor based on LSG/PBSE/PtNPs exhibited a wide range concentration with good sensitivity. Additionally, the nanostructured surface provides a suitable microenvironment for enzyme immobilization and facilitates direct electron transfer between the active site of the enzyme and the electrode [34]. The as-fabricated functionalized LSG and anchored PtNPs modified biosensor offered an improved electrochemical activity and a good platform for enzyme immobilization. PtNPs serve as an inexpensive alternative to uricase enzyme for the determination of UA. To the best of our knowledge, this is the first report of a novel LSG functionalization with PBSE strategy to achieve electrochemically stable platform capable of detecting both uric acid and glucose biomarkers. The physicochemical analyses of the fabricated biosensors were conducted using field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and electrochemical techniques.