Development of a Sensitive Electrochemical Enzymatic Reaction-Based Cholesterol Biosensor Using Nano-Sized Carbon Interdigitated Electrodes Decorated with Gold Nanoparticles

We developed a versatile and highly sensitive biosensor platform. The platform is based on electrochemical-enzymatic redox cycling induced by selective enzyme immobilization on nano-sized carbon interdigitated electrodes (IDEs) decorated with gold nanoparticles (AuNPs). Without resorting to sophisticated nanofabrication technologies, we used batch wafer-level carbon microelectromechanical systems (C-MEMS) processes to fabricate 3D carbon IDEs reproducibly, simply, and cost effectively. In addition, AuNPs were selectively electrodeposited on specific carbon nanoelectrodes; the high surface-to-volume ratio and fast electron transfer ability of AuNPs enhanced the electrochemical signal across these carbon IDEs. Gold nanoparticle characteristics such as size and morphology were reproducibly controlled by modulating the step-potential and time period in the electrodeposition processes. To detect cholesterol selectively using AuNP/carbon IDEs, cholesterol oxidase (ChOx) was selectively immobilized via the electrochemical reduction of the diazonium cation. The sensitivity of the AuNP/carbon IDE-based biosensor was ensured by efficient amplification of the redox mediators, ferricyanide and ferrocyanide, between selectively immobilized enzyme sites and both of the combs of AuNP/carbon IDEs. The presented AuNP/carbon IDE-based cholesterol biosensor exhibited a wide sensing range (0.005-10 mM) and high sensitivity (similar to 993.91 mu A mM(-1) cm(-2); limit of detection (LOD) similar to 1.28 mu M). In addition, the proposed cholesterol biosensor was found to be highly selective for the cholesterol detection

Ultra-Sensitive Immuno-Sensing Platform Based on Gold-Coated Interdigitated Electrodes for the Detection of Parathion

Pesticides are unavoidable in agriculture to protect crops from pests and insects. Organophosphates (OPs) are a class of pesticides that are more harmful because of the irreversible inhibition reaction with acetylcholinesterase enzyme, thereby posing serious health hazards in human beings. In the present work, a sensitive and selective immuno-sensing platform is developed using gold inter-digitized electrodes (Au-IDEs) as substrates, integrated with a microfluidic platform having the microfluidic well capacity of 10 µL. Au-IDE having digit width of 10 µm and gap length of 5 µm was used in this study. The surface morphological analysis by field-effect scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) revealed the direct information regarding the modification of Au-IDEs with anti-parathion (Anti-PT) antibodies. In SEM analysis, it was seen that the Au-IDE surface was smooth in contrast to the Anti-PT modified surface, which is supported by the AFM studies showing the surface roughness of ~2.02 nm for Au-IDE surface and ~15.86 nm for Anti-PT modified surface. Further, Fourier transform infra-red (FTIR) spectroscopic analysis confirms the immobilization of Anti-PT by the bond vibrations upon the successive modification of Au-IDE with –OH groups, amine groups after modifying with APTES, and the amide bond formation after incubation in Anti-PT antibody. Electrochemical impedance spectroscopy (EIS) was carried out for the electrochemical characterization and for testing the sensing performances of the fabricated electrode. The developed immuno-sensor provided a linear range of detection from 0.5 pg/L–1 µg/L, with a limit of detection (LoD) of 0.66 ng/L and sensitivity of 4.1 MΩ/ngL−1/cm2. The sensor response was also examined with real samples (pomegranate juice) with good accuracy, exhibiting a shelf life of 25 days. The miniaturized sensing platform, along with its better sensing performance, has huge potential to be integrated into portable electronics, leading to suitable field applications of pesticide screening devices

An electrochemical cholesterol biosensor based on a CdTe/CdSe/ZnSe quantum dots—poly (Propylene Imine) dendrimer nanocomposite immobilisation layer

Abstract: We report the preparation of poly (propylene imine) dendrimer (PPI) and CdTe/CdSe/ZnSe quantum dots (QDs) as a suitable platform for the development of an enzyme-based electrochemical cholesterol biosensor with enhanced analytical performance. The mercaptopropionic acid (MPA)-capped CdTe/CdSe/ZnSe QDs was synthesized in an aqueous phase and characterized using photoluminescence (PL) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), X-ray power diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy. The absorption and emission maxima of the QDs red shifted as the reaction time and shell growth increased, indicating the formation of CdTe/CdSe/ZnSe QDs. PPI was electrodeposited on a glassy carbon electrode followed by the deposition (by deep coating) attachment of the QDs onto the PPI dendrimer modified electrode using 1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC), and N-hydroxysuccinimide (NHS) as a coupling agent. The biosensor was prepared by incubating the PPI/QDs modified electrode into a solution of cholesterol oxidase (ChOx) for 6 h. The modified electrodes were characterized by voltammetry and impedance spectroscopy. Since efficient electron transfer process between the enzyme cholesterol oxidase (ChOx) and the PPI/QDs-modified electrode was achieved, the cholesterol biosensor (GCE/PPI/QDs/ChOx) was able to detect cholesterol in the range 0.1–10 mM with a detection limit (LOD) of 0.075 mM and sensitivity of 111.16 µA mM−1 cm−2. The biosensor was stable for over a month and had greater selectivity towards the cholesterol molecule

Electrochemical devices for cholesterol detection

Cholesterol can be considered as a biomarker of illnesses such as heart and coronary artery diseases or arteriosclerosis. Therefore, the fast determination of its concentration in blood is interesting as a means of achieving an early diagnosis of these unhealthy conditions. Electrochemical sensors and biosensors have become a potential tool for selective and sensitive detection of this biomolecule, combining the analytical advantages of electrochemical techniques with the selective recognition features of modified electrodes. This review covers the different approaches carried out in the development of electrochemical sensors for cholesterol, differentiating between enzymatic biosensors and non-enzymatic systems, highlighting lab-on-a-chip devices. A description of the different modification procedures of the working electrode has been included and the role of the different functional materials used has been discussed

Uric acid sensing based on sandwich carbon electrode sets decorated with gold nanoparticles

Department of Mechanical EngineeringThis study reports an enzymatic uric acid sensor with enhanced electrochemical sensing performance by electrodepositing gold nanoparticles on sandwich carbon electrodes. The improvement of sensor performance was based on the structural advantage of sandwich carbon electrode sets, consisting of suspended carbon mesh electrode (SME) and substrate bound interdigitated electrodes (IDE). The uricase enzyme was selectively immobilized to IDE and by-product generated from uricase-uric acid reaction was detected in SME to track the uric acid concentration. As the SME is completely covering the IDE, the by-product can be detected with SME before being diffused into the bulk solution. The electrode structure was fabricated using simple and cost-effective technique known as carbon-microelectromechanical-systems (C-MEMS). The polymer structure was patterned using successive photolithography and converted into carbon electrode by vacuum pyrolysis. This unique technique enabled the wafer-level fabrication of two separate but adjacent electrodesSME and IDE. To enhance the surface reactivity and surface area of electrodes, gold nanoparticles were electrodeposited to the sandwich carbon electrodes. As the surface area of IDE is larger compared to the simple planar electrode, the electrodeposition of gold nanoparticles is improved on IDE. The uricase enzyme was selectively immobilized to the IDE with selective electrochemical surface modification using aryl diazonium reduction. Uricase enzyme was selectively immobilized by bonding with diazonium deposited to IDE. The selective immobilization of enzyme allowed the maintenance of SME surface electroactivity. Uric acid sensing performance was evaluated by conducting chronoamperometry test with the sensor structure for the uric acid concentration range of 0 to 1000 ??M. From structural advantage of sandwich carbon electrodes and high electrochemical reactivity of gold nanoparticles, the developed uric acid sensor was capable of sensitive uric acid sensing with low lower limit of detection (LOD) of 6.25 ??M. As uric acid concentration of healthy person???s blood is ranged from 120 to 450 ??M, the sensing range of this uric acid sensor is appropriate in detecting uric acid concentration in human blood. The sensitivity was calculated as change in current signal per uric acid concentration change divided with sensor operation area. The sandwich electrode structure showed high sensitivity with two linear ranges of uric acid concentration. The calculated sensitivity was 742.11 ??A??mM???1??cm???2 for low concentration range (0 ??? 100 ??M) and 553.26 ??A??mM???1??cm???2 for high concentration range (100 ??? 1000 ??M).clos

Glassy Carbon: A Promising Material for Micro- and Nanomanufacturing

When certain polymers are heat-treated beyond their degradation temperature in the absence of oxygen, they pass through a semi-solid phase, followed by the loss of heteroatoms and the formation of a solid carbon material composed of a three-dimensional graphenic network, known as glassy (or glass-like) carbon. The thermochemical decomposition of polymers, or generally of any organic material, is defined as pyrolysis. Glassy carbon is used in various large-scale industrial applications and has proven its versatility in miniaturized devices. In this article, micro and nano-scale glassy carbon devices manufactured by (i) pyrolysis of specialized pre-patterned polymers and (ii) direct machining or etching of glassy carbon, with their respective applications, are reviewed. The prospects of the use of glassy carbon in the next-generation devices based on the material’s history and development, distinct features compared to other elemental carbon forms, and some large-scale processes that paved the way to the state-of-the-art, are evaluated. Selected support techniques such as the methods used for surface modification, and major characterization tools are briefly discussed. Barring historical aspects, this review mainly covers the advances in glassy carbon device research from the last five years (2013–2018). The goal is to provide a common platform to carbon material scientists, micro/nanomanufacturing experts, and microsystem engineers to stimulate glassy carbon device research