Herein we report the effect of different nucleobase pair compositions on the association-induced fluorescence enhancement property of Thioflavin T (ThT), upon binding with 20 base pair long double-stranded DNA (dsDNA). Analysis of binding and decay constants along with the association (K ass ) and dissociation (K diss ) rate constants obtained from the fluctuation in the fluorescence intensity of ThT after binding with different DNA revealed selective affinity of ThT toward AT-rich dsDNA. Molecular docking also substantiates the experimental results. We also observed that addition of orange-emitting ethidium bromide (EtBr) to cyan-emitting ThT−DNA complexes leads to bright white light emission (WLE) through Forster resonance energy transfer. Additionally, the emission of white light is far greater in the case of intra-DNA strands. Besides endorsing the binding insights of ThT to AT-rich dsDNA, the present investigations open a new perspective for realizing promising WLE from two biomarkers without labeling the DNA.

The focus of this study was to understand and unravel the interaction of silver nanoparticles (AgNPs) with different types of Deoxyribonucleic acid (DNA), mammalian and bacterial, having different base pair compositions. Binding of spherical silver nanoparticles (AgNPs) to Calf thymus (CT) DNA, Escherichia coli (EC) DNA and Micrococcus lysodeikticus (ML) DNA has been studied to gain insights into their mode of interaction and specificity. Interaction of AgNPs with synthetic DNA has also been carried out. On the basis of absorption, thermal melting, isothermal calorimetry and viscosity studies, we could establish the mode of binding and specificity of the synthesized silver nanoparticles with mammalian and bacterial DNA. Thermal melting (Tm) studies indicated a decrease in the Tm of all the DNAs, confirming the destabilization of DNA stacks on interaction with AgNPs. Comparative interaction studies with single stranded (ss) and double stranded (ds) DNAs further confirmed the specificity of the particles toward ds DNA. On the basis of the results we could confirm that the synthesized AgNPs could be used for selective detection of DNA through their DNA binding mechanism. In addition, the AgNPs-DNA complexes exhibited distinct differences in the SERS spectra making it an interesting SERS platform for identifying ds DNA. The optical and physical properties of AgNPs help in differentiating the DNAs of different base pair compositions through their binding affinity and specificity.

Here, we report for the first time, a novel and intriguing application of deoxyribonucleic acid (DNA) in the area of optics by demonstrating white light emission by tuning the emission of a nanomaterial, ZnO rods, exhibiting surface defects, in the presence of genomic Escherichia coli DNA with a comparatively high quantum efficiency. In order to understand the DNA specificity, we have also studied the interaction of ZnO with CT, and ML DNA, ss EC DNA, synthetic polynucleotides and different mononucleosides and bases. Further, in order to understand the effect of particle shape and defects present in ZnO, we have also extended our study with ZnO rods prepared at higher temperature exhibiting red emission and ZnO particles exhibiting yellow emission. Interestingly, none of the above studies resulted in white light emission from ZnO-DNA complex. Our studies unequivocally confirmed that the concentration and the nature of DNA and ZnO together plays a crucial role in obtaining CIE coordinates (0.33, 0.33) close to white light. The much enhanced melting temperature (T) of EC DNA and the energetics factors confirm enhanced hydrogen bonding of ZnO with EC DNA leading to a new emission band. Our experimental observations not only confirm the selective binding of ZnO to EC DNA but also open a new perspective for developing energy saving light emitting materials through nano-bio interactions.

A single nucleotide mismatch in a particular sequence of DNA is considered to play pivotal roles in various central biological processes and is associated with the development of several types of oncogene and genetic diseases. Hence, the identification of particular probes for DNA is of great interest in order to carry out cell imaging, drug delivery, and point of care diagnostic. Herein we report the binding interaction between DNA and tripeptide-functionalized luminescent copper nanoclusters (CuNCs) for recognition of single base pair mismatched (MM) double-stranded (ds) DNA from well-matched (WM) sequences. Isothermal titration calorimetry and UV–vis thermal denaturation established that substitution of a single well-matched GC pair in 20 base pair (bp) DNA with single pyrimidine mismatches; viz. CA, CC, and CT mispair resulted in an enhanced binding affinity of CuNCs to ds DNA. Through fluorescence correlation spectroscopy, we estimated the precise values of the binding interaction at the single-molecule resolution. Analysis of autocorrelation curves, hydrodynamic radius, and association rate constants (K ass) evidently established the higher affinity of CuNCs for the single pair MM dsDNA. The order of binding affinity of CuNCs is found to be CT MM > CA MM > CC MM > WM DNA. Competitive binding studies using Hoechst and ethidium bromide substantiate the groove binding mechanism.

The phenomenon of aggregation-induced emission (AIE) is an emerging strategy used to tune the optical properties of luminescent metal nanoclusters (MNCs). Various external factors such as cations, hydrophobicity, and solvents provide impetus for AIE in MNCs. Our present investigations delineate the remarkable tuning of the photophysical properties of weakly luminescent mercaptosuccinic acid (MSA)-templated silver nanoclusters (AgNCs). Upon AIE of AgNCs through the introduction of Zn2+ ions, the emission maximum of AgNCs was shifted from ∼465 to ∼670 nm with an unusual augmentation in photoluminescence intensities (∼3000 times). The minimization of energy dissipation due to the formation of the Zn2+-induced rigid assembly mainly accounts for these unprecedented optical signatures. As a consequence of this, the otherwise weakly emissive AgNC system (quantum yield, QY ∼ 0.1%) gets converted to a highly luminescent red-emitting Zn2+-induced AgNC assembly (Zn–AgNCs, QY ∼ 2%). Our MSA-templated AgNCs demonstrated the selectivity toward Zn2+ ions in forming the Zn–AgNC assemblies, which in turn were highly sensitive toward the pH of the medium in the pH range of 5–8.