Layered Double Hydroxides As a Method for Decorating Electrodes with Metal Particles for Sensing the Antibiotic Ornidazole
Authors: Glennon Luke Daniel , Alves Daniele , Barwa Tara , Breslin Carmel B 
Published: August 2024

The use of metallic particles and nanoparticles to improve the detection capabilities of sensors has been widely reported in literature and thus, a method of decorating electrodes reliably and easily with metallic particles is of great interest. In this regard, Layered Double Hydroxides (LDHs) are of particular interest to act as a source of metal particles. LDHs are inorganic two-dimensional compounds with the general formula [M1-x
2+M3+
x(OH)2]x+(An-)x/n.mH2O where M is two different metals and A is the intercalated anion between the stacked layers of divalent and trivalent M2+/M3+
ions to produce a 2 nanosheet structure [1]. In this study LDHs are synthesised hydrothermally, which involves placing metallic salts of the desired metals into an aqueous solution in a sealed autoclave and heating to a high temperature to produce a high vapour pressure environment. From this method various elements can be combined to produce bimetallic and trimetallic LDHs.

The obtained LDH powder is then dispersed in ethanol and water using ultrasonication and layered onto the electrode surface by means of drop-casting. It can then be easily reduced using cyclic voltammetry to act as an efficient method of decorating an electrode with metallic particles of the desired elements. In this study, a variety of layered double hydroxides were synthesised using combinations of different elements and then subsequently used to reduce metal particles onto a glassy carbon electrode.

A variety of bimetallic and trimetallic LDH compounds containing copper, iron, cobalt, and nickel were investigated. To compare the sensing capabilities of these reduced metal particles, the reduction of the antibiotic ornidazole was used as an analyte. Ornidazole is a member of the nitroimidazole antibiotic family that is heavily employed in the treatment of both human and animal infections [2]. This widespread use has led to the accumulation of the antibiotic in aquatic environments, posing a serious health risk due to its toxicity and the risk of antimicrobial resistance [3]. Thus, a sensor capable of quickly and reliably detecting the antibiotic is of great importance. To enhance the conductivity of the modified sensors, a drop-casted layer of functionalised carbon black was combined with the metallic particles.

For the detection of ornidazole, the copper-iron (CuFe) particles were concluded to be optimum, displaying a detection range of 0.2 uM to 600 uM. Characterisation studies were performed on the CuFe particles using SEM, XRD, XPS, FTIR, and EDX. Investigations were carried out into the behaviour of the sensor at varying pH values and to determine the reaction kinetics of detection. To study the selectivity of the sensor interferants were introduced to the antibiotic solution and experiments were performed in real water samples gathered from various locations.

[1] A., Karmakar, K., Kannimuthu, S., Sam Sankar, K., Sangeetha, R., Madhu, & S., Kundu. Journal of Materials Chemistry A. 2020

[2] Q. Wang, C. Wang, Q. Wang, & Z. Wang, Journal of Agricultural and Food Chemistry., 2019, 67(41), 11527-11535

[3] W. El, N. Tajat, A. Idelahcen, M. Tamimi, S. Qourzal, A. Assabbane, & I. Bakas, Microchemical Journal, 2023, 195, 109397