Au-Pt-Ni nanochains as dopamine catalysts: role of elements and their spatial distribution

Multi-element materials can improve biosensing ability as each element can catalyze different steps in a reaction pathway. By combining Pt and Ni on self-assembled 1D gold nanochains and controlling their spatial distribution, a detailed understanding of each element's role in dopamine oxidation is developed. In addition, the developed synthesis process provides a simple way to fabricate multi-element composites for electrocatalytic applications based on electrical double-layer formation on the surface of charged nanoparticles. The performance parameters of the catalyst, such as its sensitivity, limit of detection, and range of operation for dopamine sensing, are optimized by changing the relative ratios of Pt : Ni and the morphology of the Pt and Ni domains, using the developed understanding. The morphology of the domains also affects the oxidation state of Ni, which is crucial to the performance of the electrocatalyst.

Emerging 0D, 1D, 2D, and 3D nanostructures for efficient point-of-care biosensing

The recent COVID-19 infection outbreak has raised the demand for rapid, highly sensitive POC biosensing technology for intelligent health and wellness. In this direction, efforts are being made to explore high-performance nano-systems for developing novel sensing technologies capable of functioning at point-of-care (POC) applications for quick diagnosis, data acquisition, and disease management. A combination of nanostructures [i.e., 0D (nanoparticles & quantum dots), 1D (nanorods, nanofibers, nanopillars, & nanowires), 2D (nanosheets, nanoplates, nanopores) & 3D nanomaterials (nanocomposites and complex hierarchical structures)], biosensing prototype, and micro-electronics makes biosensing suitable for early diagnosis, detection & prevention of life-threatening diseases. However, a knowledge gap associated with the potential of 0D, 1D, 2D, and 3D nanostructures for the design and development of efficient POC sensing is yet to be explored carefully and critically. With this focus, this review highlights the latest engineered 0D, 1D, 2D, and 3D nanomaterials for developing next-generation miniaturized, portable POC biosensors development to achieve high sensitivity with potential integration with the internet of medical things (IoMT, for miniaturization and data collection, security, and sharing), artificial intelligence (AI, for desired analytics), etc. for better diagnosis and disease management at the personalized level.

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.

n-Butanol/Water Interface-Aided Physicochemical Tuning of Two-Dimensional Transition-Metal Oxides

Herein, we report a facile regulation of the interface of two immiscible solvents, n-butanol and water, to achieve the physicochemical tuning of the transition-metal oxide nickel cobaltite. The crystal nucleation and the growth of nickel cobaltite into distinct morphology are highly dependent on the orientation and the mass transfer of the reactive species through the reactive interface layer. A distinct two-dimensional flakelike (1 nm thickness) nickel cobaltite is formed at the interface of n-butanol/water in a 1:1 solvent ratio. Rather, one-dimensional needles and irregular interconnected networks are achieved, as aqueous and organic counterparts are, respectively, increased. The impact of the solvent ratio on doping metal ions (Co²⁺ and Ni²⁺) at the interstitial sites of fcc spinel structure is evident from the X-ray and electronic absorption investigations. It is presumed that the interface-assisted synthesis may provide a simple and novel way to develop and adopt various transition-metal oxides for wide applications.

Graphite paste electrodes modified with a sulfo-functionalized metal-organic framework (type MIL-101) for voltammetric sensing of dopamine

The metal-organic frameworks MIL-101 and sulfo-MIL-101 were used to modify graphite paste electrodes (GPEs) to obtain sensors for determination of dopamine (DA). Taking advantage of the catalytic activity of metal-organic frameworks (MOFs) and of the electrical conductivity of graphite, the modified GPEs show enhanced voltammetric responses, and the GPE modified with the sulfo-MOF displays superior sensitivity when operated at a working potential of -0.4 to 0.8 V (vs. Ag/AgCl). The sensor works in the 0.07 to100 μM DA concentration range and has a 43 nM detection limit. It is concluded that the sulfo group provides open sites for efficient electrostatic and hydrogen bonding interactions, which facilitates electron transfer. Graphical abstractSchematic representation of the structure of the sulfo-functionalized MOF (sulfo-MIL-101) and the different voltammetric signals of dopamine at the graphite paste electrodes (GPEs) modified with sulfo-MIL-101 and the parent MOF (MIL-101).

A review on electrochemical biosensing platform based on layered double hydroxides for small molecule biomarkers determination

The development of layered double hydroxides (LDHs), also known as anionic clays with uniform distribution of metal ions and facile exchangeability of intercalated anions, are now appealing an immense deal of attention in synthesis of multifunctional materials. In electrochemical biosensors, LDHs provide stable environment for immobilization of enzymes or other sensing materials and play crucial roles in development of clinical chemistry, point-of-care devices through analysis of various small molecule metabolites excreted by biological processes which in turn serve as molecular biomarkers for medical diagnostics. In this review, we summarize the recent development in fabrication of LDH based nanoarchitectures and their electrocatalytic applications in ultrasensitive in vitro determination of conventional biomarkers, i.e., H₂O₂, glucose, dopamine and other biomolecules. Moreover, detailed discussion has been compiled to differentiate electrochemical enzymatic and nonenzymatic biosensors, to evaluate useful concentration ranges of H₂O₂ and glucose for analytical circumstances and to distinguish tumorigenic and normal cells via quantifying the released H₂O₂ efflux from living cells. Here, we envision that electrochemical sensing platform based on structurally integrated LDH nanohybrids with highly conducting substrates will assist as diseases diagnostic probe further enhancing diagnosis as well as therapeutic window for chronic diseases. Finally, the perspective for fabrication and assembly of LDH electrode is proposed for the future innovation of electrochemical biosensors with high performance making them more reliable for in vitro diagnostics.

Novel electrochemical sensing platform for ultrasensitive detection of cardiac troponin I based on aptamer-MoS2 nanoconjugates

Cardiac troponin I (cTnI) is a specific and sensitive biomarker for the early diagnosis of acute myocardial infarction and for the subsequent clinical treatments. In this work, novel electrochemical sensing platform for sensing of cTnI based on aptamer-MoS₂ nanoconjugates was proposed. For comparison, core-shell Au@SiO₂@Au nanoparticles were also used for sensing of cTnI. The sensing schemes and electrochemical responses of the proposed sensors were investigated by electrochemical impedance spectroscopy (EIS) in 5.0 mM K₃[Fe(CN)₆]/K₄[Fe(CN)₆] (1:1) solution containing 0.1 M KCl, respectively. Results showed that the aptamer-Au@SiO₂@Au based aptasensor shows a linear rage of 10 pM-10.0 μM with the detection limits of 1.23 pM For the aptamer-MoS₂ nanosheets based aptasensor, the linear range for cTnI detection was from 10 pM to 1.0 μM with a lower detection limit of 0.95 pM Meanwhile, both the sensors were successfully applied for detection of cTnI in human blood samples. The two kinds of aptsensors have been successfully used for detecting of cTnI in human blood serums. Moreover, no negligible signal changes could be observed in the presence of non-targets of CK-MB and Myo, suggesting the good potential for clinic diagnosis.