Peptide-Functionalized Quantum Dots for Rapid Label-Free Sensing of 2,4,6-Trinitrotoluene.

Explosive compounds, such as 2,4,6-trinitrotoluene (TNT), pose a great concern in terms of both global public security and environmental protection. There are estimated to be hundreds of TNT contaminated sites all over the world, which will affect the health of humans, wildlife, and the ecosystem. Clearly, the ability to detect TNT in soils, water supplies, and wastewater is important for environmental studies but also important for security, such as in ports and boarders. However, conventional spectroscopic detection is not practical for on-site sensing because it requires sophisticated equipment and trained personnel. We report a rapid and simple chemical sensor for TNT by using TNT binding peptides which are conjugated to fluorescent CdTe/CdS quantum dots (QDs). QDs were synthesized in the aqueous phase, and the peptide was attached directly to the surface of the QDs by using thiol groups. The fluorescent emission from the QDs was quenched in response to the addition of TNT. The response could even be observed by the naked eye. The limit of detection from fluorescence spectroscopic measurement was estimated to be approximately 375 nM. In addition to the rapid response (within a few seconds), selective detection was demonstrated. We believe this label-free chemical sensor contributes to progress for the on-site explosive sensing.

Developing Hollow-Channel Gold Nanoflowers as Trimodal Intracellular Nanoprobes.

Gold nanoparticles-enabled intracellular surface-enhanced Raman spectroscopy (SERS) provides a sensitive and promising technique for single cell analysis. Compared with spherical gold nanoparticles, gold nanoflowers, i.e., flower-shaped gold nanostructures, can produce a stronger SERS signal. Current exploration of gold nanoflowers for intracellular SERS has been considerably limited by the difficulties in preparation, as well as background signal and cytotoxicity arising from the surfactant capping layer. Recently, we have developed a facile and surfactant-free method for fabricating hollow-channel gold nanoflowers (HAuNFs) with great single-particle SERS activity. In this paper, we investigate the cellular uptake and cytotoxicity of our HAuNFs using a RAW 264.7 macrophage cell line, and have observed effective cellular internalization and low cytotoxicity. We have further engineered our HAuNFs into SERS-active tags, and demonstrated the functionality of the obtained tags as trimodal nanoprobes for dark-field and fluorescence microscopy imaging, together with intracellular SERS.

Screening and characterisation of CdTe/CdS quantum dot-binding peptides for material surface functionalisation.

Quantum dots (QDs) are promising nanomaterials due to their unique photophysical properties. For them to be useful in biological applications, the particle surface generally needs to be conjugated to biological molecules, such as antibodies. In this study, we screened CdTe/CdS QD-binding peptides from a phage display library as linkers for simple and bio-friendly QD modification. Among five QD-binding peptide candidates, a series of truncated peptides designed from two high-affinity peptides were subjected to an array-based binding assay with QDs to assess their functional core sequences and characteristics. Linking these isolated, shortened peptides (PWSLNR and SGVYK) with an antibody-binding peptide (NKFRGKYK) created dual-functional peptides that are capable of QD surface functionalisation by antibodies. Consequently, the dual-functional peptides could mediate anti-CD9 antibody functionalisation onto CdTe/CdS QD surface; CD9 protein imaging of cancer cells was also demonstrated. Our proposed peptides offer an effective vehicle for QD surface functionalisation in biological applications.

Biogenic synthesis of silver nanoparticles from Cassia fistula (Linn.): In vitro assessment of their antioxidant, antimicrobial and cytotoxic activities.

The present study reports on biogenic-synthesised silver nanoparticles (AgNPs) derived by treating Ag ions with an extract of Cassia fistula leaf, a popular Indian medicinal plant found in natural habitation. The progress of biogenic synthesis was monitored time to time using a ultraviolet-visible spectroscopy. The effect of phytochemicals present in C. fistula including flavonoids, tannins, phenolic compounds and alkaloids on the homogeneous growth of AgNPs was investigated by Fourier-transform infrared spectroscopy. The dynamic light scattering studies have revealed an average size and surface Zeta potential of the NPs as, -39.5 nm and -21.6 mV, respectively. The potential antibacterial and antifungal activities of the AgNPs were evaluated against Bacillus subtilis, Staphylococcus aureus, Candida kruseii and Trichophyton mentagrophytes. Moreover, their strong antioxidant capability was determined by radical scavenging methods (1,1-diphenyl-2-picryl-hydrazil assay). Furthermore, the AgNPs displayed an effective cytotoxicity against A-431 skin cancer cell line by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, with the inhibitory concentration (IC50) predicted as, 92.2 ± 1.2 µg/ml. The biogenically derived AgNPs could find immense scope as antimicrobial, antioxidant and anticancer agents apart from their potential use in chemical sensors and translational medicine.

Bacterial (BKH1) assisted silica nanoparticles from silica rich substrates: a facile and green approach for biotechnological applications.

A green technique of silica nanoparticles (SiO2-NPs) formation by using a thermophilic bacterium (BKH1) as biological template is demonstrated here. SiO2-NPs are synthesized from inorganic (magnesium tri-silicate), and organic (tetraethyl orthosilicate) precursor with the help of BKH1 bacteria. BKH1 derived SiO2-NPs are subjected to Atomic Force Microscopy, Transmission Electron Microscopy, and Field Emission Scanning Electron Microscopy equipped with Energy Dispersive X-ray Analyzer to establish nanoparticle morphology. In addition, Infrared Spectroscopy reveals the presence of chemical and functional groups in SiO2-NPs samples and X-ray diffraction, the amorphous nature. The Zeta potential (ζ) reveals substantial stability of bacteria derived SiO2-NPs in the aqueous environment. Presence of two intense luminescence peaks in the UV and visible regions merits the bacteria derived SiO2-NPs for use as an optical probe in biomedical applications. This novel mode of bacteria derived SiO2-NPs formation is eco-friendly and ambient temperature synthesis approach. It avoids the complex protocol of multi-steps synthesis of silica nanoparticles, hence likely to be cost-effective. In-depth translation research is suggested for the synthesis of silica nanoparticles in large quantities using thermophilic BKH1 template.

DNA-Assisted ß-phase Nucleation and Alignment of Molecular Dipoles in PVDF Film: A Realization of Self-Poled Bioinspired Flexible Polymer Nanogenerator for Portable Electronic Devices.

A flexible nanogenerator (NG) is fabricated with a poly(vinylidene fluoride) (PVDF) film, where deoxyribonucleic acid (DNA) is the agent for the electroactive ß-phase nucleation. Denatured DNA is co-operating to align the molecular -CH2/-CF2 dipoles of PVDF causing piezoelectricity without electrical poling. The NG is capable of harvesting energy from a variety of easily accessible mechanical stress such as human touch, machine vibration, football juggling, and walking. The NG exhibits high piezoelectric energy conversion efficiency facilitating the instant turn-on of several green or blue light-emitting diodes. The generated energy can be used to charge capacitors providing a wide scope for the design of self-powered portable devices.