Browsing by Author "Ng, Zhi Kai"

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Free-Standing Three-Dimensional Graphene Scaffolds for Protease Functional Assay
(Elsevier Science Sa, 2024) Ng, Zhi Kai; Yan, Evelias; Goyal, Garima; Gudlur, Sushanth; Kanagavel, Deepankumar; Yildiz, Umit Hakan; Teo, Edwin Hang Tong
Three-dimensional graphene scaffolds (3d-GS) of high porosity possessing good fluorescence quenching properties are potential candidates for the development of optical biosensors. Herein, we demonstrate the feasibility of utilising intact and free-standing 3d-GS for sensitive detection of proteases, a class of disease diagnosis bio-markers of significant interest. Recombinant OmpT was employed as a model protease for validating the pro-posed methodology. A short (15-residue) peptide sequence encoding a specific recognition site for OmpT was end-labelled with a fluorescent dye (5-FAM) whose fluorescence is quenched when the peptide is anchored to 3d-GS. However, in the presence of OmpT, the peptide is cleaved and released from 3d-GS, resulting in a sig-nificant recovery in fluorescence. The functional assay described herein involves a single step fabrication process of anchoring the peptide to 3d-GS. The integrity of the 3d-GS is hypothesised to overcome the concern of dynamic requenching associated with the typical homogeneous assays based on graphene, yielding a limit of detection (LOD) of similar to 140 nM, which is over an order higher than homogeneous assays performed using the same composition of graphene in powdered form. To the best of our knowledge, this is the first report on utilising free-standing 3d-GS for facile assaying of proteases.
Citation - WoS: 1
Citation - Scopus: 1
A Multi-Layered Graphene Based Gas Sensor Platform for Discrimination of Volatile Organic Compounds Via Differential Intercalation
(Royal Society of Chemistry, 2023) Özkendir İnanç, Dilce; Ng, Zhi Kai; Başkurt, Mehmet; Keleş, Berfin; Vardar, Gökay; Şahin, Hasan; Tsang, Siu Hon; Palaniappan, Alagappan; Yıldız, Ümit Hakan; Teo, Eht
Selective and sensitive detection of volatile organic compounds (VOCs) is of critical importance for environmental monitoring, disease diagnosis and industrial applications. Among VOCs, assay development for primary alcohols has captured significant research attention since their toxicity causes adverse effects on gastrointestinal and central nerve systems, resulting in irreversible blindness, and coma, and can be even fatal at high exposure levels. However, selective detection of primary alcohols is extremely challenging owing to the similarity in their molecular structure and characteristic groups. Herein, we have attempted to investigate the differential methanol (MeOH)-ethanol (EtOH) discriminative properties of single-layer, bi-layer, and multi-layer graphene morphologies. Chemiresistors fabricated using the three morphologies of graphene illustrate discriminative MeOH-EtOH responses, which is attributed to the phenomenon of differential intercalation of MeOH within layered graphene morphologies as compared to that of EtOH. This hypothesis is verified by density functional theory calculations, which revealed that the adsorption of EtOH molecules on the graphene surface is more energetically favorable as compared to that of MeOH molecules, thereby inhibiting their intercalation within the layered graphene morphologies. It is further evaluated that the degree of MeOH intercalation increases with increasing layers of graphene for obtaining differential MeOH-EtOH responses. Experimental results suggest possibilities to develop selective and sensitive MeOH assays fabricated using various graphene morphologies in a combinatorial sensor array format.
Radially Aligned Carbon Nanotube Glass Fiber Composites as Ion-Selective Microelectrodes
(Amer Chemical Soc, 2025) Onder, Ahmet; Ng, Zhi Kai; Tsang, Siu Hon; Alagappan, Palaniappan; Teo, Edwin Hang Tong; Yildiz, Umit Hakan
Detection of ions is challenging due to their small size, rapid diffusion, and high mobility, especially for assaying in samples of low volumes. Among the traditional analytical methods, potentiometric ion-selective electrodes (ISE) have become a popular choice for detecting ions as they are cost-effective, user-friendly and can be miniaturized, making them useful for on-site analysis. In this context, radially aligned carbon nanotubes (RACNT) directly grown on glass fibers (GF) via the chemical vapor deposition method is investigated as a solid contact material for the fabrication of ion-selective microelectrodes (mu ISE) upon incorporating specific ionophores within a polymeric encapsulation membrane. As an illustration, sensitive detection of ammonium ions is accomplished by the fabricated mu ISE (plasticized PVC membrane containing nonactin ionophores), which yielded a LOD and a linear response range between 7.5 x 10-6 and 1.0 x 10-5 to 1.0 x 10-1 M, respectively. The mu ISE fabricated with RACNT-GF as an interface material exhibited improvements in LOD and enhanced the detection selectivity as compared to a conventional ISE fabricated using planar solid contact materials such as graphite. We hypothesize that the fabricated mu ISE with a high surface area and mechanical durability maximize the accommodation of ionophores in the barrier membrane for yielding improved potentiometric responses. Experimental results illustrate that the mu ISE possesses the potential to be utilized for the fabrication of selective and sensitive ISE upon incorporation of specific ionophores with RACNT-GF composites.