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Cellular heterogeneity poses a major challenge for tumor theranostics, requiring high-resolution intercellular bioanalysis strategies. Over the past decades, the advantages of electrochemical analysis, such as high sensitivity, good spatio-temporal resolution, and ease of use, have made it the preferred method to uncover cellular differences. To inspire more creative research, herein, we highlight seminal works in electrochemical techniques for biomolecule analysis and bioimaging. Specifically, micro/nano-electrode-based electrochemical techniques enable real-time quantitative analysis of electroactive substances relevant to life processes in the micro-nanostructure of cells and tissues. Nanopore-based technique plays a vital role in biosensing by utilizing nanoscale pores to achieve high-precision detection and analysis of biomolecules with exceptional sensitivity and single-molecule resolution. Electrochemiluminescence (ECL) technology is utilized for real-time monitoring of the behavior and features of individual cancer cells, enabling observation of their dynamic processes due to its capability of providing high-resolution and highly sensitive bioimaging of cells. Particularly, scanning electrochemical microscopy (SECM) and scanning ion conductance microscopy (SICM) which are widely used in real-time observation of cell surface biological processes and three-dimensional imaging of micro-nano structures, such as metabolic activity, ion channel activity, and cell morphology are introduced in this review. Furthermore, the expansion of the scope of cellular electrochemistry research by innovative functionalized electrodes and electrochemical imaging models and strategies to address future challenges and potential applications is also discussed in this review. [Display omitted] • Recent progress of electrochemical science biological research. • Overview of molecular detection techniques ranging from extracellular to intracellular levels. • Overview of electrochemical imaging techniques for monitoring of structural characteristics. [ABSTRACT FROM AUTHOR]

Dopamine β-hydroxylase (DBH) is involved in various neuronal transmission processes in the brain. Due to the severe diseases caused by abnormity levels of such important enzyme in human serum, sensitive and rapid detection of DBH at early stages is crucial, particularly for clinical analysis. Herein, we developed optical sensors for DBH that include the following: (i) a ratiometric fluorescence sensor that hybridizes the bovine serum albumin (BSA)-gold nanoclusters (BSA-AuNCs) and nitrogen doped carbon dots (N-CDs). The sensor proved to be highly selective and sensitive, achieving a linear range of 0.02–0.16 μg mL−1 and a limit of detection of 4.0 ng mL−1. In the presence of DBH, the fluorescence intensity of BSA-AuNCs (λ em = 615 nm) was remarkably quenched by DBH serving as a reporter signal, whereas the N-CDs fluorescence intensity at 440 nm was almost kept unchanged serving as a reference signal. The developed ratiometric sensor is capable of demonstrating a color change from pink to violet and blue with a gradual increase in DBH concentration, which is discernible by the naked-eye. A test strip is prepared for semi-quantitative assay and convenient use. Intriguingly, by taking advantage of the inter-AuNCs aggregation in the presence of DBH, (ii) a resonance light scattering (RLS) sensor was also developed based on the nanohybrid probe (detection limit 95 ng mL−1). Fluorescence imaging in PC12 cell lines demonstrated that the BSA-AuNCs could be utilized in visualization assay towards intracellular DBH. Additionally, the sensors were tested in a real matrix by spiking serum samples with satisfactory recoveries. Image 1 • Ratiometric fluorescence method for Dopamine β-hydroxylase was developed for the first time. • Dopamine β-hydroxylase assay was performed for the first time based on a nontoxic and simple method. • A resonance light scattering detection of Dopamine β-hydroxylase was developed. • A portable and visual test strip was developed for Dopamine β-hydroxylase as a point of care testing. • Cellular imaging of the BSA-AuNCs was achieved successfully on brain cells. [ABSTRACT FROM AUTHOR]

Pyrene-phenylglycinol tangled ratiometric sensor (R)-1 was developed for the detection of Al3+ ion over other metal ions. Ratiometric behaviour of (R)-1 for Al3+ ion explained through monomer emission and excimer quenching leads to avoiding the π-π interactions of bis-pyrene rings. Pull-push to push-pull binding mechanism is successfully explained by DFT and sensing of Al3+-ions demonstrated in living cells. The LOD of (R)-1 for Al3+ downs to nanomolar concentrations which is lower than the allowed concentration of drinking water set by the (World Health Organization) WHO. Image 1 • Probe (R)-1 selectively detects Al3+-ion via ratiometric approach and detection limit upto nanomolar range. • Pull-push to push-pull binding mechanism is supported by fluorimetry and DFT studies. • Probe (R)-1 act as a reversible ratiometric sensor for Al3+ ion in the presence of EDTA. • Sensing behaviours (R)-1 to Al3+ ion successfully applied into living cell imaging studies. [ABSTRACT FROM AUTHOR]

Conjugated polymers for bioimaging and sensing chemical/biological reagents have received much attention owing to their outstanding photophysical properties. However, most conventional synthetic strategies result in aggregates of conjugated polymers with limited solubility in most common organic and aqueous solvents. Therefore, advancement in molecular design and synthetic pathways is required to tune the optical and solubility properties of the resulting conjugated polymers. Herein, a simple, general, and effective approach for the synthesis of water-soluble polypyrrole (PPy) is reported based on the chemical polymerization in the presence of a homologue series of dicarboxylic acids with different chain lengths as multifunctional dopant molecules, possessing two carboxylic acid groups which serve as both dopants and stabilizing agents. The role of dopant chain length on the emission properties of resulting water-soluble polymers has been investigated. Among the synthesized water-soluble polymers, succinic acid-stabilized polymer (PPy-Suc) showed the highest emission wavelength (λ em = 453 nm), high quantum yield (12.87), very good photostability and low cytotoxicity, suggesting its applicability in bioimaging and sensing applications. As a proof of concept, the PPy-Suc polymer was successfully utilized in cellular imaging. Moreover, a novel fluorescence iodide sensor with two linear ranges of 0.012–0.200 and 0.200–8.825 μM and a low detection limit of 9 nM was developed based on the prepared PPy-Suc polymer. The superior properties of the synthesized water-soluble polymers confirm the potential applicability of developed method as a general, facile and effective synthesis approach in preparation of water-soluble conjugated polymers with several potential applications. Image 1 • PPy structure was modified with introducing homologue series of dicarboxylic acids. • Dicarboxylic acids act as both dopants and stabilizers and prepared water-soluble conjugated polymers. • The synthesized polymer (PPy-Suc) was used for development of a sensitive and selective iodide ion fluorescence sensor. • The PPy-Suc polymer was successfully utilized in cellular imaging. [ABSTRACT FROM AUTHOR]

A novel imidazo[1,2-a]pyridine-rhodamine ratiometric fluorescent probe IP-Hg for Hg2+ based on a fluorescence resonance energy transfer mechanism has been developed. The probe has been proved to show high sensitivity and high selectivity toward Hg2+. Furthermore, it could be used for imaging Hg2+ in cells and in polluted water. Image 1 • A ratiometric fluorescent probe for sensing Hg2+ based on new imidazo[1,2-a]pyridine fluorophore has been synthesized. • The probe exhibits highly sensitivity and selectivity toward Hg2+ (LOD: 9.1 nM). • The ratiometric fluorescent probe displays a remarkable emission shift (220 nm). • The probe show low cytotoxicity and can image in cells. [ABSTRACT FROM AUTHOR]

Abstract A new highly selective and sensitive dual-mode sensor 3TD based on the conjugate of oligothiophene and barbituric acid moiety was developed for colorimetric and turn-on fluorescent detection of CN─. The sensor 3TD exhibited high specificity towards CN─ by interrupting its own ICT producing thereupon a large blue-shift in UV–Vis spectrum and remarkable "turn-on" fluorescence emission. The detection limit was 2.26 × 10─7 M, which is quite lower than the permissible level of CN─ in drinking water according to the WHO. The fluorescent detection of CN─ was well demonstrated by filter paper strips and silica coated TLC plates. Moreover, the sensor was also used to detect CN─ in environmental water and agro-products with satisfactory results. Most importantly, in terms of these advantages of colorimetric and turn-on fluorescent dual-mode, immediate response, excellent selectivity, high sensitivity, low cytotoxicity, and good biocompatibility, the sensor 3TD was successfully applied into CN− imaging in living cells, demonstrating its excellent value in practical application. Graphical abstract Image 1 Highlights • A new colorimetric naked-eye and turn-on fluorescent sensor 3TD was developed. • Sensor 3TD emerged strong response to CN− with rapid, selective, and sensitive characteristics. • Sensor 3TD could detect trace CN− in water, agro-products and test strips. • Sensor 3TD showed low cytotoxicity and was successfully applied to living cell imaging. [ABSTRACT FROM AUTHOR]

The targeted labeling imaging of stellate cells on liver frozen section by immunofluorescence is a very promising visualization technique to study the distribution of stellate cells in the liver. In this study, water soluble carbon quantum dots that can emit blue, green and yellow fluorescence are synthesized by the hydrothermal method, and their sizes are 3.2, 3.7, and 4.3 nm, respectively. The three carbon quantum dots have good fluorescence stability, and the quantum yields are 36.1%, 26.3% and 21%, respectively. When the mass fraction of KCl in the blue carbon quantum dot dispersion system is 13%, it still maintains the liquid state at −30 °C. The final fluorescent probe is obtained after the carbon quantum dots are coupled with the secondary antibody, spectral characterizations confirm that the conjugate probe still maintains protein immunoactivity and has good stability. Cell experiments prove that the probe has good biocompatibility, the rabbit anti-mouse Desmin antibody is used as the primary antibody, the results of cellular immunofluorescence imaging and flow cytometry show that the probe can specifically label hepatic stellate cell at −20 °C. The results of liver frozen section experiments show that hepatic stellate cell can be specifically targeted and labeled by the fluorescent probe. This labeling technology provides an important technical means for elucidating the structure and function of the liver at the cellular level, exploring the liver pathological change, and designing and developing drug. [Display omitted] • Multicolor water-soluble carbon quantum dots were synthesized. • The fluorescence intensity of carbon quantum dots had a good temperature dependence. • Low temperature could improved the fluorescence properties of carbon quantum dots. • The fluorescence imaging of hepatic stellate cells was successfully demonstrated at −20 °C. [ABSTRACT FROM AUTHOR]

Surface modification and functionalization is typically required to engineer upconversion nanoparticles (UCNPs) for biosensing and bioimaging applications. Nevertheless, despite various antibody conjugation methods having been applied to UCNPs, no consensus has been reached on the best choice, as the results from individual studies are largely unable to be compared due to inadequate assessment of the properties of the conjugated products. Here, we introduce a systematic approach to quantitatively evaluate the biological activity of antibody-conjugated UCNPs. We determine that the optimal antibody conjugation efficiency to our colominic acid polysaccharide-coated UCNPs via 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide/N-hydroxy succinimide (EDC/NHS) coupling is approximately 70%, corresponding to 16 antibodies per nanoparticle of 63 nm hydrodynamic diameter, with on average 12 of the 16 antibodies maintaining their affinity to the target antigens. The binding ability of the antibody-conjugated UCNPs to the antigen was well preserved, as verified by enzyme-linked immunosorbent assay (ELISA), flow cytometry, and cellular imaging. This is the first study to quantitate the active antibody binding capacity of polysaccharide coated UCNP nanoparticles, offering a practical guideline for benchmarking functionalised UCNPs in future studies. • A one-phase ligand exchange method was established to derive polysaccharide coated upconversion nanoparticles. • A novel immunoassay was developed to determine the accessibility of antibodies on upconversion nanoparticles. • We determined the number of antibody conjugated on one upconversion nanoparticle as 16 and 12 of them remained active. • The binding activity were also validated by routine methods, including ELISA, flow cytometry, and cellular imaging. • The proposed workflow offers a simple and universal approach for benchmarking antibody-conjugated UCNP. [ABSTRACT FROM AUTHOR]