Metal oxide nanomaterials based electrochemical and optical biosensors for biomedical applications: Recent advances and future prospectives

The amalgamation of nanostructures with modern electrochemical and optical techniques gave rise to interesting devices, so-called biosensors. A biosensor is an analytical tool that incorporates various biomolecules with an appropriate physicochemical transducer. Over the past few years, metal oxide nanomaterials (MONMs) have significantly stimulated biosensing research due to their desired functionalities, versatile chemical stability, and low cost along with their unique optical, catalytic, electrical, and adsorption properties that provide an attractive platform for linking the biomolecules, for example, antibodies, nucleic acids, enzymes, and receptor proteins as sensing elements with the transducer for the detection of signals or signal amplifications. The signals to be measured are in direct proportionate to the concentration of the bioanalyte. Because of their simplicity, cost-effectiveness, portability, quick analysis, higher sensitivity, and selectivity against a broad range of biosamples, MONMs-based electrochemical and optical biosensing platforms are exhaustively explored as powerful early-diagnosis tools for point of care applications. Herein, we made a bibliometric analysis of past twenty years (2004-2023) on the application of MONMs as electrochemical and optical biosensing units using Web of Science database and the results of which clearly reveal the increasing number of publications since 2004. Geographical area distribution analysis of these publications shows that China tops the list followed by the United States of America and India. In this review, we first describe the electrochemical and optical properties of MONMs that are crucial for the creation of extremely stable, specific, and sensitive sensors with desirable characteristics. Then, the biomedical applications of MONMs-based bare and hybrid electrochemical and optical biosensing frameworks are highlighted in the light of recent literature. Finally, current limitations and future challenges in the field of biosensing technology are addressed.

Magnetic in situ determination of surface coordination motifs by utilizing the degree of particle agglomeration

Most analytical techniques used to study the surface chemical properties of superparamagnetic iron oxide nanoparticles (SPIONs) are barely suitable for in situ investigations in liquids, where SPIONs are mostly applied for hyperthermia therapy, diagnostic biosensing, magnetic particle imaging or water purification. Magnetic particle spectroscopy (MPS) can resolve changes in magnetic interactions of SPIONs within seconds at ambient conditions. Herein, we show that by adding mono- and divalent cations to citric acid capped SPIONs, the degree of agglomeration can be utilized to study the selectivity of cations towards surface coordination motifs via MPS. A favored chelate agent, like ethylenediaminetetraacetic acid (EDTA) for divalent cations, removes cations from coordination sites on the SPION surface and causes redispersion of agglomerates. The magnetic determination thereof represents what we call a "magnetically indicated complexometric titration". The relevance of agglomerate sizes for the MPS signal response is studied on a model system of SPIONs and the surfactant cetrimonium bromide (CTAB). Analytical ultracentrifugation (AUC) and cryogenic transmission electron microscopy (cryo-TEM) reveal that large micron-sized agglomerates are required to significantly change the MPS signal response. With this work, a fast and easy-to-use characterization method to determine surface coordination motifs of magnetic nanoparticles in optically dense media is demonstrated.

Amino-coumarin-based colorimetric and fluorescent chemosensors capable of discriminating Co2+, Ni2+, and Cu2+ ions in solution and potential utilization as a paper-based device

New chemosensors, L1-L3, based on the coumarin Schiff base scaffold with substituent modifications, have been designed and synthesized. The chemosensors L1-L3 exhibited the absorbance and fluorescence spectral changes that can discriminate Co²⁺, Ni²⁺, and Cu²⁺ ions. Sensor L1 demonstrated the ability to respond to Co²⁺, Ni²⁺, and Cu²⁺ ions. Remarkably, the slight modification of substituent on L2 has been observed to cause selective binding to Ni²⁺ and Cu²⁺ ions while L3 can specifically detect Cu²⁺ ions. The in-situ formation of metal and ligand complexes was determined by Job's plot analysis. The limit of detection and the sensing ability of all probes are estimated to be within the range of safe drinking water. Incorporation of the sensing compounds into a paper-based detection system using a laminated paper-based analytical device (LPAD) was demonstrated and found to be consistent to those obtained from the batchwise solution measurements.

Electrochemical paper-based microfluidic device for on-line isolation of proteins and direct detection of lead in urine

In this work, we developed a microfluidic paper-based analytical device (μPAD) for the on-line isolation of proteins and the electrochemical detection of lead ions (Pb(II)) in urine samples. The patterned filter paper was prepared through the direct printing of microchannel patterns on filter paper using an office laser printer. The paper was modified with protein precipitant and was then coupled with a detachable three-electrode system. Experimental parameters, namely, modification reagents, microchannel length and width, deposition potential, and deposition time, were optimized. Then, the maximum protein concentration under which the device can function was obtained as 300 mg L^-1. The linear range was 10-500 μg L^-1 with a detection limit of 9 μg L^-1. The effectiveness of this device was demonstrated through the quantification of Pb(II) in urine samples and the results agreed with those of atomic absorption spectrometry (AAS).

Fluorescence switch of gold nanoclusters stabilized with bovine serum albumin for efficient and sensitive detection of cysteine and copper ion in mice with Alzheimer's disease

The near-infrared fluorescence of gold nanoclusters stabilized with bovine serum albumin (BSA -AuNCs) centered at 675 nm could be enhanced by cysteine and then effectively quenched by copper ion (Cu²⁺), therefore, cysteine and copper ion could be detected in sequence. At "on" state, fluorescence enhancement of BSA-AuNCs is generated due to the reaction between cysteine and BSA-AuNCs, via filling the surface defect of gold nanoclusters, while Cu²⁺ can further oxidize the reductive sulfydryl of cysteine and interact with amino acids presented in the BSA chain, inducing gold nanoclusters to aggregate, thus causing "off" state with fluorescence quenching. Fluorescence switch of BSA-AuNCs can be used for cysteine and Cu²⁺ detection in mice brain with Alzheimer's disease (AD) in vitro, with fast response, high chemical stability and sensitivity. Besides, it was able to image the endogenous Cu²⁺ in liver and heart of AD mice in situ. The results are promising, especially in the framework of early diagnosis of Alzheimer's disease.

Nitrogen-doped carbon dots as a probe for the detection of Cu2+ and its cellular imaging

Nitrogen-doped carbon dots were synthesized using citric acid monohydrate and glutathione as raw materials. The synthesized nitrogen-doped carbon dots were characterized by multiple analytical techniques, including transmission electron microscopy, Fourier transform infrared spectroscopy, ultraviolet–visible absorption spectroscopy, X-ray photoelectron spectroscopy, X-ray diffractometry, and fluorescence spectra. The fluorescence intensity of the nitrogen-doped carbon dots gradually quenched with different concentrations of Cu2+ ions. The effect of the pH value, the nitrogen-doped carbon dot concentration, and the reaction time on the fluorescence intensity of the N-CDs-Cu2+ system was investigated, and the experimental conditions were optimized. A rapid and sensitive method for the determination of Cu2+ ions was established that exhibited a good linearity in the concentration range 0.20–200.0 μM with a detection limit of 0.27 nM. Meanwhile, the fluorescence quenching mechanism of the interaction between nitrogen-doped carbon dots and Cu2+ was preliminarily discussed. The method was used to detect trace Cu2+ in tap water and lake water, with recoveries ranging from 98.1% to 102.0%. Furthermore, due to low cytotoxicity and good biocompatibility, nitrogen-doped carbon dots as a probe were also successfully used in bioimaging.

A highly turn-on fluorescent CHEF-type chemosensor for selective detection of Cu2+ in aqueous media

An efficient "turn on" fluorescence chemosensor Schiff base LH based on the combination of 2-Hydroxy-5-(p-tolyldiazenyl)benzaldehyde and N-(3-Aminopropyl)imidazole was prepared and characterized then evaluated for its selective fluorescent sensing of Cu²⁺ amongst other metal ions. The CN isomerization inhibition process induced by the Cu²⁺ binding warrants the chelation-induced enhanced fluorescence (CHEF) effect. In addition, the detection limit sensing of LH for Cu²⁺ was found to be 1.8 × 10^-6 M that is below the WHO recommendation level (20 μM) for drinking water.

Enhanced In Vitro Biocompatibility and Water Dispersibility of Magnetite and Cobalt Ferrite Nanoparticles Employed as ROS Formation Enhancer in Radiation Cancer Therapy

Efficient magnetic reactive oxygen species (ROS) formation enhancing agents after X-ray treatment are realized by functionalizing superparamagnetic magnetite (Fe₃ O₄ ) and Co-ferrite (CoFe₂ O₄ ) nanoparticles with self-assembled monolayers (SAMs). The Fe₃ O₄ and CoFe₂ O₄ nanoparticles are synthesized using Massart's coprecipitation technique. Successful surface modification with the SAM forming compounds 1-methyl-3-(dodecylphosphonic acid) imidazolium bromide, or (2-{2-[2-hydroxy-ethoxy]-ethoxy}-ethyl phosphonic acid provides biocompatibility and long-term stability of the Fe₃ O₄ and CoFe₂ O₄ nanoparticles in cell media. The SAM-stabilized ferrite nanoparticles are characterized with dynamic light scattering, X-ray powder diffraction, a superconducting quantum interference device, Fourier transform infrared attenuated total reflectance spectroscopy, zeta potential measurements, and thermogravimetric analysis. The impact of the SAM-stabilized nanoparticles on the viability of the MCF-7 cells and healthy human umbilical vein endothelial cells (HUVECs) is assessed using the neutral red assay. Under X-ray exposure with a single dosage of 1 Gy the intracellular SAM stabilized Fe₃ O₄ and CoFe₂ O₄ nanoparticles are observed to increase the level of ROS in MCF-7 breast cancer cells but not in healthy HUVECs. The drastic ROS enhancement is associated with very low dose modifying factors for a survival fraction of 50%. This significant ROS enhancement effect by SAM-stabilized Fe₃ O₄ and CoFe₂ O₄ nanoparticles constitutes their excellent applicability in radiation therapy.

Highly selective and sensitive method for Cu2+ detection based on chiroptical activity of L-Cysteine mediated Au nanorod assemblies

Herein, we demonstrated a simple and efficient method to detect Cu²⁺ based on amplified optical activity in the chiral nanoassemblies of gold nanorods (Au NRs). L-Cysteine can induce side-by-side or end-to-end assembly of Au NRs with an evident plasmonic circular dichroism (PCD) response due to coupling between surface plasmon resonances (SPR) of Au NRs and the chiral signal of L-Cys. Because of the obvious stronger plasmonic circular dichrosim (CD) response of the side-by-side assembly compared with the end-to-end assemblies, SS assembled Au NRs was selected as a sensitive platform and used for Cu²⁺ detection. In the presence of Cu²⁺, Cu²⁺ can catalyze O₂ oxidation of cysteine to cystine. With an increase in Cu²⁺ concentration, the L-Cysteine-mediated assembly of Au NRs decreased because of decrease in the free cysteine thiol groups, and the PCD signal decreased. Taking advantage of this method, Cu²⁺ could be detected in the concentration range of 20pM-5nM. Under optimal conditions, the calculated detection limit was found to be 7pM.

A sensitive electrochemical sensor using an iron oxide/graphene composite for the simultaneous detection of heavy metal ions

We report an analytical assessment of an iron oxide (Fe2O3)/graphene (G) nanocomposite electrode used in combination with in situ plated bismuth (Bi) working as an electrochemical sensor for the determination of trace Zn(2+), Cd(2+), and Pb(2+). The as-synthesized nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, thermo-gravimetric analyzer, and X-ray diffraction. The electrochemical properties of the Fe2O3/G/Bi composite modified electrode were investigated. Differential pulse anodic stripping voltammetry was applied for the detection of metal ions. Due to the synergetic effect between graphene and the Fe2O3 nanoparticles, the modified electrode showed improved electrochemical catalytic activity high sensitivity toward trace heavy metal ions. Several parameters such as the preconcentration potential, bismuth concentration, preconcentration time, and pH were carefully optimized to determine the target metal ions. Under optimized conditions, the linear range of the electrode was 1-100μgL(-1) for Zn(2+), Cd(2+), and Pb(2+), and the detection limits were 0.11μgL(-1), 0.08μgL(-1), and 0.07μgL(-1), respectively (S/N =3). Repeatability (% RSD) was found to be 1.68% for Zn(2+), 0.92% for Cd(2+), and 1.69% for Pb(2+) for single sensor with 10 measurements and 0.89% for Zn(2+), 1.15% for Cd(2+), and 0.91% for Pb(2+) for 5 different electrodes. The Fe2O3/G/Bi composite electrode was successfully applied to the analysis of trace metal ions in real samples. The solventless thermal decomposition method applied to the simple and easy synthesis of nanocomposite electrode materials can be extended to the synthesis of nanocomposites and promising electrode materials for the determination of heavy metal ions.

Biomedical Perspective of Electrochemical Nanobiosensor

Electrochemical biosensor holds great promise in the biomedical area due to its enhanced specificity, sensitivity, label-free nature and cost effectiveness for rapid point-of-care detection of diseases at bedside. In this review, we are focusing on the working principle of electrochemical biosensor and how it can be employed in detecting biomarkers of fatal diseases like cancer, AIDS, hepatitis and cardiovascular diseases. Recent advances in the development of implantable biosensors and exploration of nanomaterials in fabrication of electrodes with increasing the sensitivity of biosensor for quick and easy detection of biomolecules have been elucidated in detail. Electrochemical-based detection of heavy metal ions which cause harmful effect on human health has been discussed. Key challenges associated with the electrochemical sensor and its future perspectives are also addressed.

Thio-pyridinium capped silver nanoparticle based supramolecular recognition of Cu(i) in real samples and T-lymphocytes

1-(3-(Acetylthio)propyl)-4-formylpyridinium coated silver nanoparticles were synthesized and used for the selective detection of Cu(i) to overcome Cu(i) poisoning in T-lymphocytes.

Nanoparticle electrochemistry

This perspective article provides a survey of recent advances in nanoscale electrochemistry, with a brief theoretical background and a detailed discussion of experimental results of nanoparticle based electrodes, including the rapidly expanding field of “impact electrochemistry”.

Green synthesis of gold nanoparticles and its application for the trace level determination of painter's colic

The green synthesis of metal nanoparticles is found to be more attractive in various disciplines, including in analytical chemistry for heavy metal ion sensing.

Visual and portable strategy for copper(II) detection based on a striplike poly(thymine)-caged and microwell-printed hydrogel

Due to its importance to develop strategies for copper(II) (Cu(2+)) detection, we here report a visual and portable strategy for Cu(2+) detection based on designing and using a strip-like hydrogel. The hydrogel is functionalized through caging poly(thymine) as probes, which can effectively template the formation of fluorescent copper nanoparticles (CuNPs) in the presence of the reductant (ascorbate) and Cu(2+). On the hydrogel's surface, uniform wells of microliter volume (microwells) are printed for sample-injection. When the injected sample is stained by Cu(2+), fluorescent CuNPs will be in situ templated by poly T in the hydrogel. With ultraviolet (UV) irradiation, the red fluorescence of CuNPs can be observed by naked-eye and recorded by a common camera without complicated instruments. Thus, the strategy integrates sample-injection, reaction and indication with fast signal response, providing an add-and-read manner for visual and portable detection of Cu(2+), as well as a strip-like strategy. Detection ability with a detectable minimum concentration of 20 μM and practically applicable properties have been demonstrated, such as resistance to environmental interference and good constancy, indicating that the strategy holds great potential and significance for popular detection of Cu(2+), especially in remote regions. We believe that the strip-like hydrogel-based methodology is also applicable to other targets by virtue of altering probes.

Emission tunable, cyto/hemocompatible, near-IR-emitting Ag2S quantum dots by aqueous decomposition of DMSA

Size tunable aqueous Ag2S quantum dots emitting in the near-infrared region were synthesized through decomposition of meso-2,3-dimercaptosuccinic acid (DMSA) in water. The resulting NIR QDs are highly cyto- and hemocompatible, have quantum yields as high as 6.5% and are effective optical imaging agents based on in vitro evaluation.

A fluorescence turn-on detection of copper(II) based on the template-dependent click ligation of oligonucleotides

In this work, a fluorescence turn-on method for copper(II) detection is reported. A molecular beacon (MB) was designed as a template. Cu(2+) was reduced to Cu(+) in the presence of a reductant (ascorbic acid). Two short single-stranded oligonucleotides one was labeled with a 5'-alkyne and the other with 3'-azide group, proceeded a template-dependent chemical ligation through the Cu(I)-catalyzed azide-alkyne cycloaddition. The newly generated click-ligated long chain oligonucleotide, which was complementary to the MB, opened the MB hairpin structure and resulted in a turn on fluorescence. The increase in fluorescence intensity is directly proportional to the amount of Cu(2+) added to the assay solution. The present assay is quite sensitive and allows the detection of 2 nM Cu(2+). The described assay also exhibits high selectivity over other metal ions.

A ferrocene-porphyrin ligand for multi-transduction chemical sensor development

5,10,15,20-Tetraferrocenyl porphyrin, H2TFcP, a simple example of a donor-acceptor system, was tested as ligand for the development of a novel multi-transduction chemical sensors aimed at the determination of transition metal ions. The fluorescence energy transfer between ferrocene donor and porphyrin acceptor sub-units was considered. The simultaneously measured optical and potentiometric responses of solvent polymeric membranes based on H2TFcP permitted the detection of lead ions in sample solutions, in the concentration range from 2.7 × 10(-7) to 3.0 × 10(-3) M. The detection limit of lead determination was 0.27 μM, low enough to perform the direct analysis of Pb2+ in natural waters.

Visual sensor for the detection of trace Cu(II) ions using an immunochromatographic strip

A rapid and simple immunochromatography method based on a gold nanoparticle-labeled monoclonal antibody was developed for the on-site detection of copper (Cu) in water samples. This monoclonal antibody, obtained by a cell fusion technique, recognized the Cu-ethylenediamine-N,N,N',N'-tetraacetic acid (EDTA) complex, but not metal-free EDTA, with high sensitivity and specificity. In optimized conditions, the visual limit of detection for qualitative detection of Cu(II) ions was 10 ng/mL and the LOD for semi-quantitative detection decreased to 0.45 ng/mL with the help of a scanning reader system. The detection process was achieved within 10 min with no cross-reactivity from other heavy metal ions. The recovery of the test samples ranged from 98% to 109%. To our knowledge, this antibody-based test strip for Cu(II) ions has not been previously reported. Based on the above results, this strip sensor could be used as an alternative tool for screening heavy metal pollution in the environment.

The use of magnetic nanoparticles in analytical chemistry

Magnetic nanoparticles uniquely combine superparamagnetic behavior with dimensions that are smaller than or the same size as molecular analytes. The integration of magnetic nanoparticles with analytical methods has opened new avenues for sensing, purification, and quantitative analysis. Applied magnetic fields can be used to control the motion and properties of magnetic nanoparticles; in analytical chemistry, use of magnetic fields provides methods for manipulating and analyzing species at the molecular level. In this review, we describe applications of magnetic nanoparticles to analyte handling, chemical sensors, and imaging techniques.