Recent Advances in Layered Double Hydroxide-Based Electrochemical and Optical Sensors

Layered double hydroxides (LDHs) have attracted considerable attention as promising materials for electrochemical and optical sensors owing to their excellent catalytic properties, facile synthesis strategies, highly tunable morphology, and versatile hosting ability. LDH-based electrochemical sensors are affordable alternatives to traditional precious-metal-based sensors, as LDHs can be synthesized from abundant inorganic precursors. LDH-modified probes can directly catalyze or host catalytic compounds that facilitate analyte redox reactions, detected as changes in the probe's current, voltage, or resistance. The porous and lamellar structure of LDHs allows rapid analyte diffusion and abundant active sites for enhanced sensor sensitivity. LDHs can be composed of conductive materials such as reduced graphene oxide (rGO) or metal nanoparticles for improved catalytic activity and analyte selectivity. As optical sensors, LDHs provide a spacious, stable structure for synergistic guest-host interactions. LDHs can immobilize fluorophores, chemiluminescence reactants, and other spectroscopically active materials to reduce the aggregation and dissolution of the embedded sensor molecules, yielding enhanced optical responses and increased probe reusability. This review discusses standard LDH synthesis methods and overviews the different electrochemical and optical analysis techniques. Furthermore, the designs and modifications of exemplary LDHs and LDH composite materials are analyzed, focusing on the analytical performance of LDH-based sensors for key biomarkers and pollutants, including glucose, dopamine (DA), H2O2, metal ions, nitrogen-based toxins, and other organic compounds.

Electronic Metal-Support Interactions for Electrochemiluminescence Signal Amplification

Au nanoparticle-amplified electrochemiluminescence (ECL) signals are generally realized by nanoparticle morphology modification, functionalization, and nanoalloys formation. It remains a great challenge to utilize the intrinsic catalytic activity of spherical Au nanoparticles for ECL performance improvement. In this work, we prepared the oxygen vacancy-rich CoAl-layered double hydroxide (LDH-O_v)-supported spherical Au nanoparticles via alkali etching of LDH and electrodeposition of Au nanoparticles on the surface of LDH. It was found that the luminol ECL signals of the as-prepared system were significantly enhanced by forming the strong electronic metal-support interaction (EMSI) between Au nanoparticles and LDH-O_v. The further mechanism study demonstrated that EMSI can increase the electron density of interfacial Au atom (Au^δ-) due to a redistribution of charge and promote electron transfer between Au species and LDH-O_v. This study not only introduces EMSI to the ECL field but also paves a new way to the applications of the intrinsic activity of spherical Au nanoparticles in ECL signal amplification. We anticipate that EMSI would be applied to other metal nanocatalysts for the development of highly efficient ECL systems.

Sensitive detection of prostate-specific antigen based on dual signal amplification of Fc@MgAl-LDH and NH2-MIL-101(Fe)

An electrochemiluminescence sensor was proposed for detection of prostate-specific antigen (PSA) based on dual-amplification strategy of ferrocenecarboxylic acid@MgAl layered double hydroxides (Fc@MgAl-LDH) and NH₂-MIL-101(Fe). An (Au NPs/Fc@MgAl-LDH)_n multilayer nanofilm was fabricated by a layer-by-layer self-assembly between positively charged Fc@MgAl-LDH nanosheets and negatively charged Au NPs. The multilayer nanofilms acted as nanocarriers for antibody loading and enhancers to catalyze H₂O₂ decomposition. NH₂-MIL-101(Fe) promoted the production of reactive oxygen species due to peroxidase-mimicking activity and increased immobilization of antibodies. This sensor showed a linear detection range of 0.05 pg mL^-1 to 50 ng mL^-1 with a low detection limit of 0.034 pg mL^-1. Moreover, the detection results from this sensor were consistent with data collected from a commercial immunoassay analyzer. The sensor had significant potential for PSA detection in clinical diagnostics.