Bamaprasad Bag

Rhodamine-based probes for metal ion-induced chromo-/fluorogenic dual signaling and their selectivity towards Hg(II) ion

The new signaling probes 2-6, rhodamine-B derivatives of various receptors which contain different donor atoms for effective metal ion coordination, were synthesized and their absorption as well as fluorescence spectral responses were evaluated in the presence of various metal ions. All these probes along with the reference probe 1 have exhibited optimal metal ion-induced absorption and fluorescence enhancement with Hg(II) ion in the longer wavelength region (>500 nm) in MeCN, exploiting the spectral characteristics of metal ion-induced structural transformation of rhodamine. The selectivity and sensitivity towards Hg(II) ion were better pronounced in MeCN-H(2)O (1 : 1 v/v) medium, implying the role of the solvent molecules, water in particular, in the preferential Hg(II) coordination environment. Complexation of Hg(II) to 1-6 not only enhanced the absorption at ~560 nm, which turned the colourless solution into pink to facilitate a naked eye detection, but also amplified the fluorescence intensity simultaneously to offer high sensitivity of detection at lower concentration. The Hg(II)-induced photo-physical spectral responses of 1-6 in presence of other competitive metal ions rendered their high selectivity towards Hg(II). Further, their reversible dual channel signaling pattern under the action of counter anions, exploiting coordination tendency of anions towards Hg(II), which compete with probe-metal interaction, implied the reversibility in their Hg(II) coordination. The selectivity, sensitivity and reversibility, in principle, establishes the potential of these probes as chemosensors for Hg(II) ion detection.

A rhodamine based “off-on” probe for selective detection of Hg(II) and subsequent L-proline and 4-hydroxyproline discrimination

A substituted rhodamine based bifunctional chemosensor 2 showed “turn-on” chromogenic and fluorogenic dual mode signal modulation upon selective binding with Hg(II) whereas its Hg(II) complex selectively detects L-proline among all biologically significant amino acids by quenching of its enhanced fluorescence. In the process of ‘Off-On-Off’ signaling, the complex therefore discriminates L-proline and its hydroxyl derivative, which is a vital phenomenon of inducing selectivity among amino acid identification.

Good's buffer derived highly emissive carbon quantum dots: excellent biocompatible anticancer drug carrier

Here, a facile one-step approach has been developed for the synthesis of carbon quantum dots (CQDs) from Goods buffer. The as-synthesized CQDs emit a bright greenish blue coloured fluorescence after exposure to a 365 nm UV-lamp illumination. The bright fluorescence nature of the CQDs has proven them to be excellent probes for cellular imaging. The CQDs are highly biocompatible in nature, which has been validated by an MTT assay test. The in vitro MTT assay demonstrates a more than 95% survival rate when HEK293 (human embryonic kidney) and H357 (human oral squamous carcinoma) cells were treated with CQDs. The low cytotoxicity of Goods buffer derived CQDs opens the door to biomedical applications. The anticancer drug doxorubicin (DOX) was successfully loaded on the CQDs and their delivery efficiency to the target cells via in vitro treatment of cancerous cells was explored. The CQDs supported DOX showed a higher killing rate of the cancer cells compared to bare DOX due to its ease of internalization and efficient pH-triggered release inside the cells.

Photoelectrocatalytic oxidation of NADH by visible light driven plasmonic nanocomposites

Here, we report the efficient photoelectrocatalytic oxidation of NADH by plasmonic nanocomposites driven by visible light. The reduction in the recombination of photogenerated holes and electrons expedite the electrocatalytic oxidation process, which substantially decreases the overpotential and increases the oxidation current.

Switching selectivity between Pb2+ and Hg2+ ions through variation of substituents at xanthene end; ‘turn-on’ signalling responses by FRET modulation

Few rhodamine based probes (L1–L4) that consist of a similar 2-(aminoethyl)-pyridine unit at their carboxamide end but vary with substituents attached to the N-atom at their xanthene end were synthesized. Rhodamine G based probes L1–L3 have shown preferential chromogenic and fluorogenic ‘turn-on’ spectral responses in the presence of Pb2+ ions, where one of the two ethyl substituted secondary amino groups attached to the xanthene core either remains un-substituted (as in L1) or is functionalized with a bulky aromatic group (as in L2) or a long alkyl chain (as in L3). On the contrary, the L4 probe that incorporates two ethyl-substituents at both N-atoms attached to the xanthene core has selectively exhibited a dual mode spectral amplification in the presence of Hg2+ ions. The reversible selective dual mode signalling pattern of bifluorophoric L2 in the presence of Pb2+ ions is because of the perturbation of the combined PET (photo-induced electron transfer) inhibition and FRET (fluorescence resonance energy transfer) initiation processes. The observed ratiometric signalling pattern enabled it to detect Pb2+ ions at a low concentration level, even in living organisms such as E. coli. The altered selectivity in the signalling pattern infers a modulated stereo-electronic environment for metal ion coordination, which in turn is caused by induced amine rigidity at the xanthene end.

Solvent mediated tuning of selectivity in a rhodamine based probe and bioimaging for Pb(II) detection in plant tissues

A substituted rhodamine based probe, which exhibits dual mode signalling responses of altered selectivity as a function of variation in solvent medium, demonstrates its utility as an imaging agent for the determination of Pb(II) accumulation in the roots of Aerva lanata plant species.

Signalling probes appended with two rhodamine derivatives: inter-component preferences, Fe(III)-ion selective fluorescence responses and bio-imaging in plant species

The photophysical investigation of two amino-alkyl receptor-based probes, 1 and 2, appended with two different rhodamine derivatives but differing in their receptor constituents revealed their selective absorption and fluorescence signalling responses to Fe(III) among all metal ions investigated. Although the output channels in the complexation-induced signalling patterns of these probes are in proximity to each other, the spectroscopic signatures of Fe(III)-complexation spiro-ring opening of the individual rhodamine derivatives and associated kinetic measurements revealed a preferential coordination affinity of the rhodamine 6G (Rho-6G) component over the rhodamine-B (Rho-B) segment. The Fe(III)-selective signalling response was observed to be higher in flexible DETA(bis(2-aminoethyl)amine) receptor-incorporated probe 1 than in 2, which incorporates a rigid ethylenediamine receptor. The ratio of the fluorescence of the two wavelength output channels arising from the two different signalling subunits in the architectures of these probes enhances their sensitivity levels in Fe(III) ion detection. The utility of the Fe(III)-complexation-induced orange fluorescence output of 1 was demonstrated in the detection and localization of bio-accumulated Fe(III) ions in root tissues of Grevillea pteridifolia plant species.