Cobalt Sulfide Nanosheets as Peroxidase Mimics for Colorimetric Detection of l-Cysteine

Abstract

The rich chemical, physical, electronic, and surface properties of two-dimensional (2D) materials have witnessed an explosion of research leading to enrichment in the 2D family of materials. Cobalt sulfide (Co x S y ), a transition metal chalcogenide, has attracted significant interest as its different stoichiometric and non-stoichiometric phases offer diverse properties. To date, the Co3S4 phase has seen limited developments with recent reports suggesting good catalytic properties of this material. In the current study, we show the facile synthesis of phase pure 2D Co3S4 nanosheets using a hydrothermal approach and demonstrate the importance of the chemical reactivity of the surface atoms in achieving target selectivity during sensing. First, the catalytic activity of Co3S4 nanosheets was observed to follow Michaelis–Menten kinetics, suggesting that the nanosheets mimic the catalytic activity of the natural peroxidase enzymes. The presence of dangling sulfur atoms on the surface of the Co3S4 nanosheets allowed them to specifically interact with l-cysteine amino acid that resulted in the temporary loss of its catalytic activity. This interaction allowed us to develop a “turn-off” colorimetric sensor to detect l-cysteine even in complex mixtures of amino acids and other sulfur containing compounds. In-depth understanding of the sensor mechanism revealed a reversible competition between l-cysteine and peroxidase substrates for binding to the Co3S4 nanosheets. Due to the higher affinity of l-cysteine to the nanosheets, it first binds to the Co3S4 nanosheets blocking its nanozyme activity. Subsequently, the outstanding catalytic activity of 2D Co3S4 nanosheets assists in the oxidation of l-cysteine, and as oxidized products leave the nanozyme surface, its catalytic activity resumes. The findings of our study are likely to instigate further research into the exploration of the chemical reactivity of 2D surfaces for diverse applications.

Mechanism and Application of Surface-Charged Ferrite Nanozyme-Based Biosensor toward Colorimetric Detection of l-Cysteine

“…The LOD of the l -Cys is calculated to be 0.119 μM based on the 3σ/slope role, which is at a relatively low level compared with previous colorimetric detection of l -Cys by nanozymes (Table ). ,− …”

“…47 Therefore, the accurate sensing of L-Cys under physiological conditions is significant to evaluate human health. Previously, a variety of nanozymes (reduced graphene oxide derivative, 37 Fe 3 O 4 magnetic nanoparticles, 47 nickel oxide nanoflowers, 48 CuMnO 2 nanoflakes, 49 cobalt sulfide nano-sheets, 50 vanadium tetrasulfide, 51 CeO 2 /CoO, 52 MoS 2 −Au@ Pt, 53 and Cu@Au(Ag)/Pt 54 ) have been exploited to detect the L-Cys concentration. However, the limit of detection (LOD) or the linear range of most nanozymes is generally at relatively high levels.…”

Pore-confined cobalt sulphide nanoparticles in a metal–organic framework as a catalyst for the colorimetric detection of hydrogen peroxide

“…It is worth mentioning that ideally, the concentration range used for such kinetic studies should be located between 0.5 K m and 5 K m of the targeted substrate; 49 previous studies reporting the use of cobalt sulphide-based materials for the TMB/H 2 O 2 reaction also utilized similar concentration ranges for kinetic studies. 46,47 Herein, the use of a H 2 O 2 concentration higher than 45 mM would reduce the reliability of the collected UV-vis data owing to the fast initial reaction rate, and the use of a TMB concentration higher than 0.6 mM exceeds the solubility limit for TMB. Therefore, data of initial reaction rates collected within 25-45 mM and 0.4-0.6 mM were used for the kinetic studies of H 2 O 2 and TMB, respectively.…”

“…6 Thereafter, the cobalt-functionalized MOF-808 (Co-MOF-808) powder was immersed into a solution containing thioacetamide (TAA) as the sulphur source, where the chemical bonds between the cobalt ions and hexa-zirconium nodes were dissociated; the formation of cobalt sulphide nanoparticles that are selectively confined within the pore of MOF-808 could thus occur. Since cobalt sulphide has been reported as a catalyst to catalyse the oxidation of chromogenic substrates, e.g., 3,3 0 ,5,5 0 -tetramethylbenzidine (TMB), in the presence of H 2 O 2 , [44][45][46][47] as a demonstration here, the obtained pore-confined cobalt sulphide nanoparticles in MOF-808 served as the catalyst for the colorimetric detection of H 2 O 2 .…”

“…Since cobalt sulphide has been reported as a catalyst to catalyse the oxidation of chromogenic substrates, e.g. , 3,3′,5,5′-tetramethylbenzidine (TMB), in the presence of H 2 O 2 , 44–47 as a demonstration here, the obtained pore-confined cobalt sulphide nanoparticles in MOF-808 served as the catalyst for the colorimetric detection of H 2 O 2 .…”