Boron carbon oxyphosphide heterostructured nanodots with phosphate tunable emission for switchable dual detection channels of 6-mercaptopurine assay.

The preparation of boron-carbon-oxygen (BCO)-based heterostructure needs commonly high temperature, high pressure and/or auxiliary strong oxidant. And the BCO-based probe for the sensing application is still rare owing to their few active groups, low quantum yield or missing specificity. Exploring BCO-based heterostructured probe via simple routes and application in sensing, therefore, is highly challenging. Herein, we proposed a novel boron-carbon-phosphorus-oxygen (BCPO) nanodot with phosphate tunable near-ultraviolet emission performance and narrow full width at half maximum by a facile, green and gentle synthesis process. The BCPO not only exhibits a distinctive colorimetric response to 6-mercaptopurine (6-MP), but also displays 6-MP-sensitive photoluminescence quenching. Thus, dual detection channels for 6-MP based on BCPO probe have been developed, and the mechanism has been speculated. Enrichment-electron of the 6-MP can be adsorbed at the boron vacancy orbits of the BCPO by the chemical action. The formation of 6-MP/BCPO complexes trigger the efficient photoluminescence quenching and light-absorbing enhancing of the BCPO, owing to the synergistic effect of the acceptor-excited photo-induced electron/energy transfer, inner filter effect and p/π-π conjugated stacking. Furthermore, the presence of ClO- anion efficaciously sparks the release of the 6-MP molecule from the 6-MP/BCPO complexes, thereby a rapid photo-switch of the BCPO for the 6-MP has been developed. Thus, this study can not only guide the further rational design of the BCPO probe, but also inspire the in-depth application of the BCPO and other nanomaterial-based probes.

Excitation-independent emission carbon nanoribbon polymer as a ratiometric photoluminescent probe for highly selective and sensitive detection of quercetin.

In this study, sulfur-nitrogen co-doped carbon nanoribbon (SNCNR) polymers with stable dual-emission fluorescence were synthesized using a one-step traditional hydrothermal method of 6-mercaptopurine in an aqueous methanol solution. Unexpectedly, the as-prepared SNCNRs with excitation-independent emission, as carbon nanomaterial derivatives, showed stable dispersions of a reticular-like shape and different lengths in the skeleton diameter. Compared with other carbon nanomaterials, the SNCNRs dramatically improved the electronic properties and surface chemical reactivities, and exhibited a sensitive ratiometric response to quercetin (Que) because of the Meisenheimer-like complexes formed through π-π stacking and electrostatic interaction. By using this SNCNR sensor, excellent ratiometric linear relationships (FL345 nm/FL420 nm) existed between the degree of quenching of the SNCNRs and the concentrations of Que in the range of 50.0 nM to 200 µM, and the limit of detection was 21.13 nM (3σ/k). Meanwhile, this sensor shows high selectivity for Que over other biomolecules, most amino acids and metal ions under the same conditions. Finally, this fluorescent probe was successfully applied to the direct analysis of Que in bovine serum and some beverage samples, which showed that it has potential for use in applications in clinical diagnosis and food analysis, and may pave the way for the design of effective fluorescent probes for other biologically related targets and food protection.

Carbon nanospheres with dual-color emission and their application in ratiometric pyrophosphate sensing.

Herein, we employ pH-dependent solubility equilibrium to develop the one-pot aqueous synthesis of dual-color emission fluorescent carbon nanosphere (DFCSs) with novel physicochemical properties. Unexpectedly, some of the DFCSs have a regular nanosphere shape, containing uniform carbon dots (∼20 nm) on their surface. This may be attributed to the change in the surface composition of the carbon nanospheres under the strong alkaline conditions (pH 13), which results in dual-wavelength emission by single-wavelength excitation. Interestingly, the fluorescence intensities of the two emission peaks of the DFCSs at 315/410 nm can be simultaneously quenched upon the addition of Co2+ due to the strong coordination between Co2+ and the O-containing luminescent groups from the carbon dots and DFCSs. Also, the results demonstrate that one Co2+ simultaneously combines with two chromophoric groups. Furthermore, the quenched DFCSs exhibit high sensitivity for pyrophosphate (PPi) in the range of 0.075-200.0 µM through a fluorescence recovery process, which can be attributed to the stronger Co2+-O[double bond, length as m-dash]P bond. This results in the removal of Co2+ from the surface of DFCSs-Co2+ system via competitive adsorption interactions. Meanwhile, this sensor shows high selectivity for PPi over mercapto amino acid and phosphate in aqueous solution. These results indicate the DFCSs can act as a dual-signal PPi-selective sensor via a ratiometric competitive mechanism.

Photoluminescent coral-like carbon-branched polymers as nanoprobe for fluorometric determination of captopril.

The authors describe the synthesis of fluorescent coral-like carbon nano-branched polymers (PCNBPs) co-doped with nitrogen and phosphorus. Uric acid and phosphoric acid act as nitrogen and phosphorus sources, respectively. The PCNBPs have a coral-like branched structure, are cross-connected, and < 20 nm in skeleton diameter. Their blue fluorescence, best measured at excitation/emission wavelengths of 330/425 nm, is quenched by mercury (II) ions due to the specifically restricted rigid conformation caused by the interaction of phosphorus, nitrogen, and oxygen groups on the surface of the PCNBPs. Fluorescence is selectivity quenched by Hg(II) but restored in addition of the hypertension drug captopril (CAP) in the range 50 nM to 40 µM concentration range. Fluorescence recovery is attributed to the effectively specific interactions between the thiol group of CAP and Hg(II). The method was applied to the determination of the concentration of Cap in pharmaceutical samples, and recoveries were between 97.6 and 105.1%. Graphical abstract Fluorescent coral-like carbon nano-branched polymers (PCNBPs) co-doped with nitrogen and phosphorus are described. Their fluorescence is selectivity quenched by Hg(II) but restored in addition of the hypertension drug captopril (Cap) in the range 50 nM to 40 µM concentration range.

Multiplexed ratiometric photoluminescent detection of pyrophosphate using anisotropic boron-doped nitrogen-rich carbon rugby ball-like nanodots.

The shape of nanoparticles is decisive for their intrinsic physicochemical properties, as well as for the anisotropic behavior of individual particles in many instances. Herein, boron-doped nitrogen-rich carbon rugby ball-like nanodots (BNCRDs) have been synthesized by a heterophase polymerization route at a vital mass ratio of phenylboronic acid and uric acid in the precursor solution. Unexpectedly, the as-prepared BNCRDs showed stable dispersions of ellipsoidal carbonaceous polymer nanodots (rugby ball-like structures that are approximately 150 nm in length) as novel carbon dot derivatives. The anisotropic BNCRDs are water-soluble compounds that have highly enhanced photoluminescence (PL), which is accompanied by a large red shift of the emission peak upon the addition of Hg2+ and is nearly quenched upon the addition of Cu2+. This is due to the chelation-enhanced fluorescence property of the BNCRDs following Hg2+ complexation with sterically efficient heteroaromatics in the BNCRDs and the chelation enhancement quenching effect of the BNCRDs following Cu2+ complexation with the N/O donor atoms of the surface of the BNCRDs, respectively. Importantly, the BNCRD PL, which is changed by Hg2+ and Cu2+, exhibits high selectivity and sensitivity for the pyrophosphate ion (PPi) in the ranges 50 nM-280 µM and 10 nM-100 µM through a photoluminescent reset process, respectively, and could be attributed to the effective coordination/chelation interactions between Hg2+/Cu2+ and the plentiful oxygen groups of PPi. These results indicate that anisotropic BNCRDs can act not only as a ratiometric sensor for Hg2+ but also as a dual-mode PPi-selective sensor via ratiometric displacement and a competitive mechanism. With the broad diversity in the molecular backbone of the carbon dots via rich chemical routes, anisotropic BNCRDs have been developed with unique structural, electrical, and attractive functions, which greatly expands the research horizon of carbon-based composites.