Ultrasensitive Enzyme-free Biosensor by Coupling Cyclodextrin Functionalized Au Nanoparticles and High-Performance Au-Paper Electrode

Abstract

Microfluidic paper-based analytical device (μPAD), originally developed for improving healthcare in developing countries, presents a simple yet powerful platform for performing low-cost and portable diagnostic devices. Here, we report an enzyme-free μPAD for the detection of two tumor markers. First, a porous structure of gold nanoparticle (AuNP)-modified paper working electrode (Au-PWE), with a feature of all-round conductivity and plenty of active sites favoring biological ligand attachment, was fabricated as a sensor substrate. Next, cyclodextrin functionalized AuNPs (CD@AuNPs) as dual mimicking enzyme were prepared to load secondary antibodies or peptide. On one sample zone, in the presence of carcinoembryonic antigen (CEA), CD@AuNPs could be introduced into the Au-PWE through a sandwich immunoreaction, boosting the electrochemical signal of o-phenylenediamine (o-PD) via the trigger of a cascade catalysis reaction toward glucose and o-PD, eventually resulting in the sensitive detection of CEA. On another working zone, with the introduction of another target prostate-specific antigen (PSA), peptide cleavage took place, which further led to CD@AuNPs being released from Au-PWE, and then, the variation of electrochemical signals was recorded for the detection of PSA. We demonstrated, using the device, that the detection of CEA and PSA clinically had high sensitivity, wide linear ranges, and low detection limits. We believe that our work provides a promising platform for point-of-care testing, especially in resource-limited regions.

Applications of Gold Nanoparticles in Non-Optical Biosensors

“…Studies show that the catalytic activity of AuNPs arises from their quantum scale, high surface-to-volume ratio and interface-dominated property, which is able to reduce the overpotential of electrochemical reactions and accelerate the chemical reaction, leading to the improvement of detection sensitivity. Typically, AuNPs are used to catalyze redox reactions such as nicotinamide adenine dinucleotide (NADH), hydrogen peroxide (H 2 O 2 ), 4-nitrophenol, o-phenylenediamine (o-PD), catechol and nitrite [118,119,120].…”

An Ultra-Rapid Biosensory Point-of-Care (POC) Assay for Prostate-Specific Antigen (PSA) Detection in Human Serum

“…For example, a conductivity PSA paper biosensor was reported by Ji et al [ 9 ] using anti-PSA antibody-bioactivated multiwall carbon nanotubes (LOD = 1.18 ng/mL, assay time = 2 h). Zheng et al [ 10 ] developed an all-around conductive microfluidic paper-based analytical device (μPAD) with cyclodextrin-functionalized gold nanoparticles (CD@AuNPs) immobilized on the paper working electrode via a custom peptide (CEHSSKLQLAK-NH2). When present in the sample, PSA cleaved the peptide, resulting in measurable changes in current flowing through the electrode (LOD = 1 pg/mL, assay time > 40 min).…”

Flexible Electronics Based on Micro/Nanostructured Paper

“…Thus, such substrates have made significant contributions to wearable and portable electronic systems by improving the bendability, expanding the integration possibilities, reducing the weight, and lowering the cost ( Figure ). These benefits originate from the natural attributes and unique structural features of paper: 1) paper is a ubiquitously available and renewable material with low cost; 2) because it is biocompatible, biodegradable, and combustible, paper can be safely disposed of by incineration, saving space in e‐waste disposal; 3) liquid substances can flow in defined channels via capillary action without relying on external forces;[6a,31] 4) the properties (e.g., hydrophilicity and permeability) of the paper matrix can be tailored to meet individual demands; 5) the 3D porous structure throughout the thickness of the paper with a high surface area allows functional reagents to be easily absorbed, and most importantly, two sides of the paper can be selectively treated with different or same functions; 6) cellulose being not soluble in classical organic solvents endows paper with excellent chemical stability; and 7) paper consisting of only cellulose exhibits higher dimensional stability over temperature and lower thermal expansion than most of plastics, making it possible to be functionalized (or operated) at elevated temperatures, which is advantageous for electronic components without introducing complex thermal parasitic effects in the electronic devices' behavior.…”

“…Notably, this redundant steps can be omitted by utilizing an all‐in‐one conductive gold electrode. In this case, the abovementioned steps were repeated several times to allow the seed and nutritional solution soak the entire thickness of the paper substrate through the capillary action and gravity . Finally, the desired paper electrodes were fabricated with all‐around conductivity.…”

“…Due to their distinctive physical and chemical properties, including superior conductivity, good biocompatibility, facile morphology and size control, and long‐term stability, gold nanostructures (NPs, NRs, and flower‐like shapes) have been fabricated in the form of an interconnected network by in situ growth strategy and employed as working electrodes on designed lab‐on‐paper device . As illustrated in Figure b,c, no apparent structural difference was found between the raw paper and seed coated cellulose because the Au NPs were smaller in size than the original cellulose fibers (tens of micrometers in diameter).…”