A Luminescence Assay in the Red for the Detection of Hydrogen Peroxide and Glucose Based on Metal Coordination Polyelectrolyte-Induced Supramolecular Self-Assembly of Alkynylplatinum(II) Complexes

A new sensing strategy towards hydrogen peroxide based on metal coordination polyelectrolyte-driven self-assembly of alkynylplatinum(II) 2,6-bis(benzimidazol-2'-yl)pyridine (bzimpy) complex was demonstrated. The cationic in situ-generated Ag(I)-thiocholine coordination polyelectrolytes were shown to induce the supramolecular self-assembly of anionic low-energy red-emissive alkynylplatinum(II) bzimpy complexes via non-covalent Pt(II)⋅⋅⋅Pt(II), electrostatic and π-π stacking interactions. The presence of hydrogen peroxide was shown to inhibit the formation of coordination polyelectrolytes and the coordination polyelectrolyte-induced self-assembly of platinum(II) complexes. The weakening of Pt(II)⋅⋅⋅Pt(II), electrostatic and π-π stacking interactions was supported by UV-vis absorption, emission, and resonance light scattering (RLS) studies. The present assay was also applied to probe glucose indirectly based on the enzymatic reaction of glucose oxidase on the substrate. Operating in a label-free manner, together with the low-energy red emission and large Stokes shift of alkynylplatinum(II) complexes, these features render the proposed design attractive for biological applications.

Highly dispersive Pt-Pd nanoparticles on graphene oxide sheathed carbon fiber microelectrodes for electrochemical detection of H2O2 released from living cells

We report a facile strategy for the synthesis of surfactant-free, small and highly dispersive Pt-Pd nanoparticles on graphene oxide (Pt-Pd NPs/GO) by an electroless deposition method, which is sheathed on carbon fiber microelectrodes (CFMs) as an electrochemical sensing platform for highly sensitive and selective detection of hydrogen peroxide (H₂O₂) released from the living cells. GO serves as the reducing agent and stabilizer for electroless deposition of Pd NPs on the surface of GO owing to its low work function (4.38 eV) and highly conjugated electronic structure. The obtained Pd NPs/GO have a relatively high work function (4.64 eV), and thereby could be used as stabilizer for synthesis of surfactant-free, small and highly dispersive Pt-Pd NPs/GO by chemical reduction of K₂PtCl₄. The obtained Pt-Pd NPs have a uniform size of 4.0 ± 0.6 nm on the surface of GO. Moreover, the Pt-Pd NPs/GO sheathed CFMs exhibit an excellent electrocatalytic activity for the reduction of H₂O₂ with a low detection limit of 0.3 μM and good selectivity. These good properties enable the modified microelectrode to detect the H₂O₂ released from living cells.

The Chemistry of Europium(III) Encountering DNA: Sprouting Unique Sequence-Dependent Performances for Multifunctional Time-Resolved Luminescent Assays

Screening functional DNA that can fruitfully interact with metal ions is a long-standing hot topic in the fields of biotechnology, medicine, and DNA-based sensors. In this paper, we focus on the chemistry of europium(III) (Eu) coupled with single-stranded DNA (ssDNA), and we innovatively unveil that cytosine- and thymine-rich ssDNA oligomers (e.g., C₁₆ and T₁₆) can be effective antenna ligands to sensitize the luminescence of Eu. Luminescence lifetime spectroscopy, circular dichroic (CD) spectroscopy, and isothermal titration calorimetry (ITC) have been used to systematically characterize the interaction involved between Eu and ssDNA. In light of the resultant sequence-dependent performances, the long luminescence lifetime Eu/ssDNA-based label-free and versatile probes are further devised as a pattern distinction system for time-resolved luminescent (TRL) sensing applications. The interactions of metal ions and ssDNA can distinctively shift the antenna effect of ssDNA toward Eu as accessible pattern signals. As a result, as few as two Eu/ssDNA label-free TRL probes can discriminate 17 metal ions via principal component analysis (PCA). In addition, thiols can readily capture metal ions to switch the luminescence of Eu/ssDNA probes initially altered by metal ions. Hence, four Eu/ssDNA-metal ion ensembles are demonstrated to be a powerful label-free TRL sensor array for pattern differentiation of eight thiols and even chiral recognition of cysteine enantiomers with different concentrations. Moreover, the sensitive TRL detection of thiols in biofluids can be successfully realized by using our method, promising its potential practical usage. This is the first report of a ssDNA-sensitized Eu-based TRL platform for label-free yet multifunctional background-free sensing and would open a door for sprouting of more novel lanthanide ion/DNA-relevant strategies toward widespread applications.

Non-enzymatic electrochemical hydrogen peroxide biosensor based on reduction graphene oxide-persimmon tannin‑platinum nanocomposite

Hydrogen peroxide (H₂O₂) is one of the most universal and essential ingredients in distinct biological tissues. Herein, a novel non-enzymatic sensor based on reduction graphene oxide-persimmon tannin‑platinum nanocomposite (RGO-PT-Pt) was exploited for H₂O₂ detection. RGO-PT-Pt nanocomposite was prepared by reduction procedure with ascorbic acid as reducing agent and characterized by Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), ultraviolet visible spectroscopy (UV-vis) and Fourier infrared spectroscopy (FT-IR). Taking advantage of high electro-catalytic efficiency of Pt nanoparticles, high electronic conductivity and large surface area of RGO, and significant adsorption ability of PT on metal ions and its prevention of agglomeration to promote RGO dispersion, RGO-PT-Pt nanocomposite revealed better catalytic ability towards H₂O₂ via a synergistic effect. Under the optimal conditions, the RGO-PT-Pt non-enzymatic biosensor exhibited outstanding electrocatalytic activity towards H₂O₂ reduction. The amperometric response demonstrated a linear relationship with H₂O₂ concentration from 1.0 to100 μM with the correlation coefficient of 0.9931. The limit of detection was 0.26 μM (S/N = 3) and the response time was 3 s. Furthermore, the fabricated sensor exhibited a practical applicability in the quantification of H₂O₂ in human serum samples with an excellent recovery rate. Due to excellent performance such as fast response time, low detection limit, high stability and selectivity, the RGO-PT-Pt non-enzymatic biosensor has potential application in clinical diagnostics.

Bioinspired Copolymers Based Nose/Tongue-Mimic Chemosensor for Label-Free Fluorescent Pattern Discrimination of Metal Ions in Biofluids

There is a close correlation between body health and the level of biofluid-derived metal ions, which makes it an attractive model analyte for noninvasive health monitoring. The present work has developed a novel nose/tongue-mimic chemosensor array based on bioinspired polydopamine/polyethylenimine copolymers (PDA/PEI _n) for label-free fluorescent determination of metal ions in biofluids. Three types of PDA/PEI _n (PDA/PEI₆, PDA/PEI₁₈, and PDA/PEI₄₈) were prepared by using different concentrations of PEI to construct the proposed sensor array, which would lead to unique fluorescence response patterns upon challenged with metal ions for their pattern discrimination. The results show that as few as 3 PDA/PEI _n sensors can successfully realize the largescale sensitive detection of metal ions in biofluids. Moreover, we have demonstrated that PDA/PEI _n sensors are qualified for lifetime-based pattern discrimination application. Furthermore, the sensors can distinguish between different concentrations of metal ions, as well as a mixture of different metal ions in biofluids, even the mixtures with different valence states. The method promises the simple, rapid, sensitive, and powerful discrimination of metal ions in accessible biofluids, showing the potential applications in the diagnosis of metal ion-involved diseases.

Nanoporous PdCu alloy as an excellent electrochemical sensor for H2O2 and glucose detection

Nanoporous (NP) PdCu alloy is easily fabricated by dealloying PdCuAl ternary alloy in dilute sulfuric acid. Selectively dissolving Al from PdCuAl alloy generates the three-dimensional uniform nanosponge architecture with narrow ligament size distribution. Benefitting from the unique nanoporous architecture and the alloying effect, the as-made NP-PdCu exhibits outstanding sensing performance towards the detection of hydrogen peroxide (H₂O₂) and glucose. Compared with NP-Pd and commercial Pd/C catalysts, the NP-PdCu alloy presents high sensitivity, wide linear range of 0.1-2.0mM, low detection limit of 2.1μM, and long-term stability toward H₂O₂ detection. In addition, the NP-PdCu can efficiently detect glucose in a wide concentration range (1-30mM) with the low detection limit of 1.9μM. Moreover, the NP-PdCu exhibits good anti-interference toward ascorbic acid, uric acid, and dopamine. Characterized by easy preparation, unique electrocatalytic activity, and high structure stability, the NP-PdCu alloy possesses great application prospect to construct platform for electrochemical sensing.

Label-free DNA-based biosensors using structure-selective light-up dyes

Label-free biosensors (LFBs) have demonstrated great potential in cost-effective applications. This review collected the latest reported works which employed structure-selective nucleic acid dyes for the development of DNA-based LFBs.