A nuclear-localized fluorescent light-up probe, NucFP-NO 2 , was designed and synthesized that can detect CO selectively in an aqueous buffer (pH 7.4, 37 °C) through the CO-mediated transformation of the nitro group into an amino-functionalized moiety. This probe triggered a more than 55-fold "turn-on" fluorescence response to CO without using any metal ions, e.g., Pd, Rh, Fe, etc. The enhanced response is highly selective over a variety of relevant reactive oxygen, nitrogen, and sulfur species and also various biologically important cationic, anionic, and neutral species. The detection limit of this probe for CO is as low as 0.18 μM with a linear range of 0−70 μM. Also, this fluorogenic probe is an efficient candidate for monitoring intracellular CO in living cells (RAW 264.7, A549 cells), and the fluorescence signals predominantly localize in the nuclear region.

An example of an aggregation‐induced emission enhancement (AIEE)‐active new naphthalene appended Schiff base (H2L) as an Al3+ ion selective fluorescent sensor has been successfully designed and synthesized. H2L showed turn‐on fluorescence at high concentration in DMF only, and at low concentration in DMF‐H2O mixtures having high water content (more than 20%). But at very low concentration of H2L and in DMF/H2O solutions with low water fraction (fw ≤ 20%), the fluorescence was turned ON in presence of Al3+ ions, which helps to detect Al3+  ions as low as 4.9×10−7 M with high selectivity in an DMF solution without any interference of other competitive metal ions. The fluorescence of H2L in different conditions and in solid state due to AIE effect has been established with the help of detailed spectroscopic studies, dynamic light scattering (DLS), scanning electron microscope (SEM), life time using time‐resolved photoluminescence and optical fluorescence microscope. The experimentally observed H‐type aggregation nature of the probe H2L has also been supported by the theoretical (DFT studies and TDDFT) studies. This probe (H2L) has also been employed for on‐site Al3+ ions detection in solid state.

A new structurally characterised half-condensed Schiff base (HL′) and a Zn2L4 complex reacting from Zn²⁺ ion and HL produced from HL′ in a solution state as smart chemosensors for Zn²⁺ and H₂PO₄⁻ ions respectively in aqueous medium.

A coumarin-based fluorescent compound, bilirubin fluorescent probe N-oxide (BFPNox), was successfully designed and synthesized for highly selective and sensitive detection of free bilirubin with short response time. The fluorescence "turn-on" response of the probe is based on the in situ generated Fe 2+mediated deoxygenation reaction of N-oxide from the diethylarylamine group of the probe, where the group attached to the coumarin π-conjugated system is responsible for the fluorescence quenching state of the probe, BFPNox. Here, the reaction of the added Fe 3+ ions with bilirubin produces Fe 2+ ions in situ in aqueous buffer. Fluorescence enhancement of BFPNox was achieved by more than 12-fold when a double equivalent of bilirubin solution was added in reaction buffer at pH 7.2 (50 mM HEPES, 5% DMSO) at 25 °C under excitation at 400 nm. It detected free bilirubin as low as 76 nM in an aqueous system without any interference of metal ions, anions, and other important biomolecules with a linear concentration range of 0−10 μM (R 2 = 0.991). The probe was also employed in the estimation of free bilirubin in human serum specimens to verify the efficacy of this probe. With these, it is revealed that this probe is a good candidate to be used as a powerful diagnostic tool for the assessment of free bilirubin with significant accuracy and reliability.

A new lysosome-targetable fluorescence sensor, Lyso-HGP, was designed and synthesized based on 4-methyl-2,6-diformylphenol as a fluorophore. Lyso-HGP displays highly sensitive fluorescent detection of Hg 2+ in HEPES buffer solution (10 mM, DMSO 1%) of pH 7.0 at 37 °C due to the formation of highly fluorescent formyl-functionalized derivative Lyso-HGP-CHO. The sensor triggered a "turn-on" fluorescence response to Hg 2+ with a simultaneous increase of fluorescence intensity by 180-fold just after 10 min. The response is very selective over a variety of biologically relevant cations, anions, molecules, and competitive toxic heavy metal cations. The limit of detection (LOD) was calculated as low as 6.82 nM. So, it can be utilized to detect this toxic heavy metal in biology and environmental samples in an aqueous buffer medium. Also, the sensor is able to monitor the subcellular distribution of Hg 2+ specifically localized in the lysosome's compartment in the MCF7 human breast cancer cell line by fluorescence microscopy.