Macromolecular Systems with MSA-Capped CdTe and CdTe/ZnS Core/Shell Quantum Dots as Superselective and Ultrasensitive Optical Sensors for Picric Acid Explosive.

This work reports the development of highly fluorescent materials for the selective and efficient detection of picric acid explosive in the nanomolar range by fluorescence quenching phenomenon. Poly(vinyl alcohol) grafted polyaniline (PPA) and its nanocomposites with 2-mercaptosuccinic acid (MSA)-capped CdTe quantum dots (PPA-Q) and with MSA-capped CdTe/ZnS core/shell quantum dots (PPA-CSQ) are synthesized in a single step free radical polymerization reaction. The thermal stability and photo stability of the polymer increases in the order of PPA < PPA-Q < PPA-CSQ. The polymers show remarkably high selectivity and efficient sensitivity toward picric acid, and the quenching efficiency for PPA-CSQ reaches up to 99%. The detection limits of PPA, PPA-Q, and PPA-CSQ for picric acid are found to be 23, 1.6, and 0.65 nM, respectively, which are remarkably low. The mechanism operating in the quenching phenomenon is proposed to be a combination of a strong inner filter effect and ground state electrostatic interaction between the polymers and picric acid. A portable and cost-effective electronic device for the visual detection of picric acid by the sensory system is successfully fabricated. The device is further employed for quantitative detection of picric acid in real water samples.

A supramolecular nanobiological hybrid as a PET sensor for bacterial DNA isolated from Streptomyces sanglieri.

The development of a rapid, label free, cost effective and highly efficient sensor for DNA detection is of great importance in disease diagnosis. Herein, we have reported a new hybrid fluorescent probe based on a cationic curcumin-tryptophan complex and water soluble mercapto succinic acid (MSA) capped CdTe quantum dots (QDs) for the detection of double stranded DNA (ds DNA) molecules. The cationic curcumin-tryptophan complex (CT) directly interacts with negatively charged MSA capped quantum dots via electrostatic coordination, resulting in photoluminescence (PL) quenching of QDs via the Photoinduced Electron Transfer (PET) process. Further, addition of ds DNA results in restoration of PL, as CT would intercalate between DNA strands. Thus, this process can be utilized for selective sensing of ds DNA via fluorescence measurements. Under optimized experimental conditions, the PL quenching efficiency of QDs is found to be 99.4% in the presence of 0.31 × 10(-9) M CT. Interestingly, the regain in PL intensity of QD-CT is found to be 99.28% in the presence of 1 × 10(-8) M ds DNA. The detection limit for ds DNA with the developed sensing probe is 1.4 × 10(-10) M. Furthermore, the probe is found to be highly sensitive towards bacterial DNA isolated from Streptomyces sanglieri with a detection limit of 1.7 × 10(-6) M. The present work will provide a new insight into preparation of bio-inspired hybrid materials as efficient sensors for disease diagnosis and agricultural development.