An electrochemiluminescence biosensor for sensitive and selective detection of Hg2+ based on π-π interaction between nucleotides and ferrocene-graphene nanosheets

Design, synthesis and evaluation of liver-targeting fluorescent probes for detecting mercury ions

Three fluorescent glycosyl-rhodamine probes with good selectivity and sensitivity toward Hg²⁺ were developed. The detection limit of the probes toward Hg²⁺ is as low as 94.6 nM, which can be used to detect trace Hg²⁺ in solution. 1 : 1 stoichiometry was the most possible recognition mode of the probes toward Hg²⁺, and the OFF/ON mechanism of the probes toward Hg²⁺ could be attributed to the closing or opening of the rhodamine spiral structure caused by Hg²⁺. The detection of Hg²⁺ is reversible, which is beneficial for the recycling of probes. Moreover, these low cytotoxic probes can be safely and selectively applied to monitor Hg²⁺ levels in hepatocytes, and the fluorescence response follows a trend of Rho-Gal > Rho-Lac > Rho-Glu in HepG2 cells because the galactose group in Rho-Gal can selectively recognize ASGPR overexpressed on HepG2 cells.

Nontraditional Redox Active Aliphatic Luminescent Polymer for Ratiometric pH Sensing and Sensing-Removal-Reduction of Cu(II): Strategic Optimization of Composition

Here, redox active aliphatic luminescent polymers (ALPs) are synthesized via polymerization of N,N-dimethyl-2-propenamide (DMPA) and 2-methyl-2-propenoic acid (MPA). The structures and properties of the optimum ALP3, ALP3-aggregate and Cu(I)-ALP3, ratiometric pH sensing, redox activity, aggregation enhanced emission (AEE), Stokes shift, and oxygen-donor selective coordination-reduction of Cu(II) to Cu(I) are explored via spectroscopic, microscopic, density functional theory-reduced density gradient (DFT-RDG), fluorescence quenching, adsorption isotherm-thermodynamics, and electrochemical methods. The intense blue and green fluorescence of ALP3 emerges at pH = 7.0 and 9.0, respectively, due to alteration of fluorophores from -C(═O)N(CH₃ )₂ / -C(═O)OH to -C(O^- )═N⁺ (CH₃ )₂ / -C(═O)O^- , inferred from binding energies at 401.32 eV (-C(O^- )═N⁺ (CH₃ )₂ ) and 533.08 eV (-C(═O)O^- ), significant red shifting in absorption and emission spectra, and peak at 2154 cm^-1 . The n-π* communications in ALP3-aggregate, hydrogen bondings within 2.34-2.93 Å (intramolecular) in ALP3 and within 1.66-2.89 Å (intermolecular) in ALP3-aggregate, respectively, contribute significantly in fluorescence, confirmed from NMR titration, ratiometric pH sensing, AEE, excitation dependent emission, and Stokes shift and DFT-RDG analyses. For ALP3, Stokes shift, excellent limit of detection, adsorption capacity, and redox potentials are 13561 cm^-1 /1.68 eV, 0.137 ppb, 122.93 mg g^-1 , and 0.33/-1.04 V at pH 7.0, respectively.

Switchable electrochemiluminescence aptasensor coupled with resonance energy transfer for selective attomolar detection of Hg2+ via CdTe@CdS/dendrimer probe and Au nanoparticle quencher

In the present study, an ultrasensitive electrochemiluminescence (ECL) aptasensing assay for selective detection of Hg²⁺ was designed. In this electrochemiluminescence resonance energy transfer (ECL-RET) approach, Fe₃O₄@SiO₂/dendrimers/QDs exhibited amplified ECL emissions (switch "on" state) and with the hybridization between T-rich ssDNA(S₁) immobilized on the Fe₃O₄@SiO₂/dendrimers/QDs and AuNPs modified with complementary aptamer (AuNPs-S₂), the ECL of QDs nanocomposites was efficiently quenched (switch "off" state). In the presence of Hg²⁺ ions, formation of strong and stable T-Hg²⁺-T complex led to the release of the AuNPs-S₂ from double-stranded DNA(dsDNA) and the recovery of the ECL signal of QDs (second signal switch "on" state). Under optimal conditions, Hg²⁺ can be detected in a wide linear range from 20aM to 2µM with a very low detection limit of 2aM. The proposed ECL aptasensor showed high selectivity for Hg²⁺ determination compared to other environmentally relevant metal ions at concentration ratio more than 1000 times. The aptasensor was used for detection Hg²⁺ ions from samples of tap waters, carp and saltwater fishes with satisfactory results. The aptasensor exhibited high sensitivity, wide linear response (11 orders of magnitude), excellent reproducibility and stability. The proposed aptasensor will be a promising candidate for facile and rapid determination of Hg^2＋in environmental and fishery samples.

Polyaniline-Stabilized Intertwined Network-like Ferrocene/Graphene Nanoarchitecture for Supercapacitor Application

The present work highlights the effective H-π interaction between metallocenes (ferrocene; Fc) and graphene and their stabilization in the presence of polyaniline (PANI) through π-π interactions. The PANI-stabilized Fc@graphene nanocomposite (FcGA) resembled an intertwined network-like morphology with high surface area and porosity, which could make it a potential candidate for energy-storage applications. The relative interactions between the components were assessed through theoretical (DFT) calculations. The specific capacitance calculated from galvanostatic charging/discharging indicated that the PANI-stabilized ternary nanocomposite exhibited a maximum specific capacitance of 960 F g^- at an energy density of 85 Wh Kg^-1 and a current density of 1 A g^- . Furthermore, electrochemical impedance spectroscopy (EIS) analysis confirmed the low internal resistance of the as-prepared nanocomposites, which showed improved charge-transfer properties of graphene after incorporation of Fc and stabilization with PANI. Additionally, all electrodes were found to be stable up to 5000 cycles with a specific capacitance retention of 86 %, thus demonstrating the good reversibility and durability of the electrode material.

Ferrocene-graphene sheets for high-efficiency quenching of electrochemiluminescence from Au nanoparticles functionalized cadmium sulfide flower-like three dimensional assemblies and sensitive detection of prostate specific antigen

A signal-switchable electrochemiluminescence (ECL) aptasensor was presented for sensitive prostate specific antigen (PSA) assay using ferrocene-graphene sheets (Fc-GNs) for high-efficiency quenching of ECL from Au nanoparticles functionalized cadmium sulfide flower-like three dimensional (3D) assemblies (Au-CdS flower-like 3D assemblies). Au-CdS flower-like 3D assemblies were synthesized and employed as luminophore, exhibiting strong and stable ECL intensity, and followed by assembling captured DNA (cDNA) and hybridizing it with half of base sequence of PSA aptamer on the Au-CdS flower-like 3D assemblies modified electrode. The remaining part of the non-complementary base of the aptamer could preferentially adsorb GN with the signal switched "off" state. While in the presence of the PSA, the binding of PSA with aptamer caused desorption of aptamer from the surface of Fc-GNs and was then released from electrode surface, thus allowing the ECL signal enhancement. With the transformation of luminescence signal from "off" to "on", the aptasensor displays high sensitivity for PSA detection with a linear range from 1pgmL^-1 to 25ngmL^-1 and a detection limit of 0.38pgmL^-1S/N=3). Moreover, this developed method could be successfully applied to the determination of PSA in human serum samples with recoveries of 85.8-104.0%, suggesting great potential applications in biochemical analysis.

Multicolour fluorescent carbon nanoparticle probes for live cell imaging and dual palladium and mercury sensors

Carbon based nanomaterials are emerging as a desirable alternative to semiconducting quantum dots due to their unique optical properties and biocompatibility. The present study demonstrates the design and synthesis of highly fluorescent carbon nanoparticles (CNPs). The CNPs are investigated for their biocompatibility and henceforth successfully employed as promising multicolor bioimaging probes in A375 and DU145 cell lines. Furthermore, a "turn off" mode has been established for the detection of noble metal palladium (Pd²⁺) and heavy metal mercury (Hg²⁺) by quenching the fluorescence of CNPs. The CNP sensor responded to the detection of Pd²⁺ (5-100 μM) and Hg²⁺ (1-18 μM) in a wide range with the limit of detection (LOD) of 58 nM for Pd²⁺ and 100 nM for Hg²⁺. The CNP sensor was employed for the detection of Pd²⁺ and Hg²⁺ in real water samples and detection of leftover palladium catalysts in a model reaction system. Also, the CNPs were successfully employed as intracellular mercury and palladium sensors using confocal microscopy.

A biocompatible cerasome based platform for direct electrochemistry of cholesterol oxidase and cholesterol sensing

An electrochemical platform composed of a biocompatible cerasome and cholesterol oxidase for cholesterol sensing.

CdS-modified porous foam nickel for label-free highly efficient detection of cancer cells

CdS-modified foam nickel (FN) was successfully constructed for the effective detection of cancer cells based on an electrochemiluminescence (ECL) technique and provides a new platform for the realization of an ECL sensor for cancer cells.

Synthesis of a carbon-dot-based photoluminescent probe for selective and ultrasensitive detection of Hg2+ in water and living cells

Nitrogen and sulphur co-doped carbon dots with high PL quantum yield and photostability have been synthesized by a simple hydrothermal synthesis and successfully used for bioimaging of Hg²⁺ in living cells.

Electrodeposition synthesis of reduced graphene oxide–carbon nanotube hybrids on indium tin oxide electrode for simultaneous electrochemical detection of ascorbic acid, dopamine and uric acid

Reduced graphene oxide–carbon nanotube (rGO–CNT) hybrids have been synthesized by electrodeposition of GO stabilized CNT using indium tin oxide (ITO) as working electrode, followed by electrochemical reduction of GO–CNT into rGO–CNT.

One-step click engineering considerably ameliorates the practicality of an unqualified rhodamine probe

This study describes the exploitation of click chemistry in the one-step molecular engineering of an unqualified rhodamine probe, leading to its considerable functional enhancement in terms of water solubility, ion selectivity, and usefulness in detecting biological and environmental samples. A dipropargyl rhodamine dye previously identified as an unselective and poorly water-soluble mercury(II) probe was used to couple with an azido polyethylene glycol (PEG) by the Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition click reaction in almost quantitative yield. The simple click-engineered rhodamine probe shows, remarkably, better water solubility and mercury(II) selectivity comparing to the raw counterpart, and can be used to sensitively image mercury ions internalized by live cells and to accurately quantify the ion spiked in river water specimens. This study provides insights into the simple functional improvement of unqualified molecular dye probes via the efficient "click engineering".

Ruthenium polypyridine complexes combined with oligonucleotides for bioanalysis: a review

Ruthenium complexes are among the most interesting coordination complexes and they have attracted great attention over the past decades due to their appealing biological, catalytic, electronic and optical properties. Ruthenium complexes have found a unique niche in bioanalysis, as demonstrated by the substantial progress made in the field. In this review, the applications of ruthenium complexes coordinated with polypyridine ligands (and analogues) in bioanalysis are discussed. Three main detection methods based on electrochemistry, electrochemiluminescence, and photoluminscence are covered. The important targets, including DNA and other biologically important targets, are detected by specific biorecognition with the corresponding oligonucleotides as the biorecognition elements (i.e., DNA is probed by its complementary strand and other targets are detected by functional nucleic acids, respectively). Selected examples are provided and thoroughly discussed to highlight the substantial progress made so far. Finally, a brief summary with perspectives is included.