Prabhpreet Singh

We have reported perylene tetra‐(alkoxycarbonyl) (PTAC) derivative PTE‐EA functionalized with tetraoctylester chains at the peri ‐positions and an electron‐donating group 2‐aminoethanol (2‐AE) at the mono bay ‐position. PTE‐EA showed colorimetric and fluorescence turn‐on response for detection of cupric ions (Cu ²⁺ ) in binary aqueous–organic mixtures. Upon Cu ²⁺ addition, the solution PTE‐EA in 30% HEPES buffer (4‐(2‐hydroxyethyl)‐1‐piperazineethanesulfonic acid)–CH ₃ CN (pH 7.3) showed a decrease in intramolecular charge transfer (ICT) absorption band at 536 nm with an increase in perylene's absorption at 460 nm. Significant fluorescence enhancement at 520 nm via inhibition of the acceptor‐excited photoinduced electron transfer (PET) process from 2‐AE to the electron‐deficient perylene core was observed. Upon Cu ²⁺ complexation, the increases in HOMO–LUMO energy gap from 2.689 to 2.824 eV and lowering of the HOMO energy from −5.350 to −10.766 eV supported the experimental bathochromic shift in the absorption maxima and thermodynamically unfavorable PET enabled fluorescence turn‐on response, respectively. The formation of the PTE‐EA ‐Cu ²⁺ complex was further corroborated by dynamic light scattering (DLS) studies, and cyclic voltammetric (CV) profile exhibited marked alterations. Also, PTAC as mono‐brominated PTE‐II with inherent solid emission was used to visualize latent fingerprints (LFPs) both under 365 nm and daylight to achieve second level of information.

Perylene diimide (PDI)-based indicator displacement assays (IDA) including metal complexes for the detection of biological analytes, metal ions and anions have been discussed.

Serum albumins, such as bovine serum albumin (BSA) and human serum albumin (HSA), play a crucial role in various biological processes. Discrimination between BSA and HSA is challenging due to their similar structures and reactivity. Here, we report mitochondria-targeted red fluorescent tripodal nanoprobe DMAS-TP, forming spherical nano-aggregates (∼90 nm) in water for discrimination of BSA over HSA and detection and imaging of viscosity in HeLa cells. DMAS-TP exhibits an ∼56-fold fluorescence intensity increase in 95% glycerol compared to water, which indicates restricted movement in high-viscosity solvents. Furthermore, the addition of 5 equiv. BSA and HSA to DMAS-TP solution displays ∼50-fold and ∼10-fold fluorescence intensity increases at 630 nm (λ_ex 490 nm), respectively, and can detect as low as 20 nM BSA and 140 nM HSA. The fluorescence anisotropy plot shows that the DMAS-TP anisotropy values decrease from 0.234 to 0.185 with increasing [BSA/HSA], suggesting a conformational change from Y- to ω-like structure. The fluorescence lifetime of DMAS-TP increases gradually with BSA/HSA, suggesting dynamic complexation. DMAS-TP aggregates diminish to 6 nm particles when encapsulated in BSA confirmed by DLS, SEM, and TEM, with reduced fluorescence intensity in the presence of bilirubin, indicating that DMAS-TP binds within the BSA cavity near site IB. DMAS-TP is highly permeable to HeLa cells and shows a strong affinity for mitochondria, making it suitable for imaging viscosity and BSA via strong fluorescence in the red channel.

We report the multistep synthesis of small molecule based yellow color powder ( VT1 ) consisting of thiourea and ─NO ₂ groups for the detection of CN ⁻ in a 10% HEPES buffer–CH ₃ CN solution and for the visualization of the latent fingerprints (LFPs) in daylight using powder dusting method. The minimum limit of detection for CN ⁻ ion is 1.47 × 10 ⁻⁷ M. We demonstrated the suitability of VT1 powder for the development and visualization of the LFPs on porous, nonporous surfaces to obtain information of levels 1–3 and for airlifting of developed fingerprints using adhesive scotch‐tape. VT1 is nontoxic and biocompatible with HeLa cells (IC ₅₀ = 48.77).

The reaction‐based probe perylene diimide–hydroxyphenyl benzothiazole (PR) can be used for the detection and discrimination of H₂S, DTT and Cys in 20% HEPES buffer–DMSO and DMSO. The H₂S induced radical anion formation of PR in 20% HEPES buffer and thiolysis of the ether bond of PR in DMSO. However, the addition of DTT showed only a decrease in the absorbance intensity and Cys showed insignificant behaviour towards PR in DMSO. The optical, AFM and DLS studies along with isolation of the reaction product in the model reaction support the interaction of the PR with bio thiols.

Herein, we have reported the design and synthesis of Perylene tetra-(alkoxycarbonyl) (PTAC) derivative PTE-EA functionalized with tetraoctyl ester chains at the peri-positions and an electron donating/recognition group 2-aminoethanol (2-AE) at the mono bay-position. PTE-EA acted as colorimetric (visual color change of the solution from light-purple to yellowish-green) and fluorescence turn-on sensing probe for the molecular recognition of Cu2+ in binary aqueous-organic mixtures. The incremental addition of Cu2+ to the solution of PTE-EA in HEPES:CH3CN (3:7, v/v, pH 7.3) showed decrease in the ICT absorption band at 536 with new blue shifted absorption band (Δλ = 76 nm) at 460 nm. Further complexation with Cu2+ result in the significant enhancement of the fluorescence intensity at 520 nm (λex = 490 nm) via inhibition of the acceptor-excited photo-induced electron transfer (a-PET) process from 2-AE to the electron-deficient perylene tetraoctyl ester core. PTE-EA showed its applicability as a colorimetric/fluorometric probe for the detection of Cu2+ by adopting two conventional photophysical mechanism viz. ICT and a-PET and demonstrated high sensitivity with nano-molar detection limits (colorimetric = 18 nM and fluorometric = 16 nM) and the complex PTE-EAꓵCu2+ showed high association constant 4.3x106 M. Further, increase in the size after complexation revealed by the DLS data. Additionally, the other derivative of PTAC as bay-functionalized mono-brominated PTE-II with strong inherent solid-state fluorescence explored for the development of latent fingerprints (LFPs) on common household surfaces and visualized in the daylight by using naked eyes and under 365 nm UV lamp and we successfully achieved 2nd level of information from the data.

Bio-thiols such as cysteine (Cys), homocysteine (Hcy), glutathione (GSH) and hydrogen sulphide (H2S) play an essential role in many physiological processes. They behave as biomarkers in many diseases, help in maintaining redox homeostasis, are associated with neurodegenerative disorders and are actively involved as enzyme active sites and cofactors. Therefore, it is important to develop efficient methods for monitoring bio-thiol levels in the intracellular environment. Analytical instrumentation-based techniques are expensive, require trained individuals and are unsuitable for on-site and point-of-care testing, so tremendous efforts have been put into the development of fluorescent sensors for detection of bio-thiols because of their low cost, sensitivity, non-invasiveness and applicability in the intracellular medium. The design of fluorescent probes for bio-thiol recognition should take into consideration the nucleophilic or reducing nature of the thiol groups. However, a real challenge is to differentiate among bio-thiol molecules. In this chapter, we focus our discussion on the detection and differentiation of bio-thiols and mechanistic details underlying the recognition process.