Purnima Neogi

Spatial Mapping of Lipids at Cellular Resolution in Embryos of Cotton

The visualization of storage, membrane, and signaling lipid species in embryos of cottonseeds at cellular resolution suggests that lipid species, even those in the same class, are distributed heterogeneously in tissues. This work provides new information about metabolite distribution and points to a previously unknown complexity in cellular biochemistry within plant tissues. Advances in mass spectrometry (MS) have made comprehensive lipidomics analysis of complex tissues relatively commonplace. These compositional analyses, although able to resolve hundreds of molecular species of lipids in single extracts, lose the original cellular context from which these lipids are derived. Recently, high-resolution MS of individual lipid droplets from seed tissues indicated organelle-to-organelle variation in lipid composition, suggesting that heterogeneity of lipid distributions at the cellular level may be prevalent. Here, we employed matrix-assisted laser desorption/ionization–MS imaging (MALDI-MSI) approaches to visualize lipid species directly in seed tissues of upland cotton (Gossypium hirsutum). MS imaging of cryosections of mature cotton embryos revealed a distinct, heterogeneous distribution of molecular species of triacylglycerols and phosphatidylcholines, the major storage and membrane lipid classes in cotton embryos. Other lipids were imaged, including phosphatidylethanolamines, phosphatidic acids, sterols, and gossypol, indicating the broad range of metabolites and applications for this chemical visualization approach. We conclude that comprehensive lipidomics images generated by MALDI-MSI report accurate, relative amounts of lipid species in plant tissues and reveal previously unseen differences in spatial distributions providing for a new level of understanding in cellular biochemistry.

Self-assembled deoxyguanosine based molecular electronic device on GaN substrates

Nanoscale hybrid molecular organic photodetectors based on self-assembled guanosine molecules conjugated to wide-bandgap GaN semiconductors has been realized in the ultraviolet wavelength regime. Metal-semiconductor-metal based photodetector is fabricated using ordering of modified guanosine based semiconductor nanowires which exhibit I-V characteristics with high current response and higher rectification ratio compared to Si based hybrid photodetectors. Photocurrent response of a two-terminal device shows the typical characteristics of a semiconductor photodiode with a cutoff wavelength at ∼325nm. The I-V characteristics have been elucidated using the induced polarization properties of self-assembled guanosine semiconductor.

Second harmonic imaging of plants tissues and cell implosion using two-photon process in ZnO nanoparticles

The optical properties of colloidal ZnO nanoparticle (NP) solutions, with size ranging from several nm to around 200 nm, have been tailored to have high optical nonlinearity for bioimaging with no auto-fluorescence above 750 nm and minimal auto-fluorescence below 750 nm. The high second harmonic conversion efficiency enables selective tissue imaging and cell tracking using tunable near-infrared femtosecond laser source ranging from 750-980 nm. For laser energies exceeding the two-photon energy of the bandgap of ZnO (half of 3.34 eV), the SHG signal greatly decreases and the two-photon emission becomes the dominant signal. The heat generated due to two-photon absorption within the ZnO NPs enable selective cell or localized tissue destruction using excitation wavelength ranging from 710-750 nm.

Bioimaging Using the Optimized Nonlinear Optical Properties of ZnO Nanoparticles

Nonlinear imaging using nanocrystals has advantages over fluorescent dyes. Highly nonlinear optically susceptible ZnO was synthesized for the purpose of bioimaging. ZnO nanoparticles with enhanced second and third order nolinearity have been utilized for nonlinear in vitro imaging of living cells. Highly efficient nonlinear processes in noncentrosymmetric ZnO nanoparticles was used to generate second harmonic signal within nanoparticles at extremely low-input light intensities in order to track and image live cells and thrombocytes infiltrated with ZnO.

Silver nanostructure sensing platform for maximum-contrast fluorescence cell imaging

We present herein a silver nanostructure-assisted sensing platform which consists of a combined structure of Ag nanowire (NW) and nanodot (ND) array. Highly enhanced fluorescence from fluorophore is attributed to a strongly coupled optical near-field interaction between proximately located Ag NW and NDs. We obtained enhanced fluorescence intensity with up to 140 folds, as contrasted from background intensity, reaching a theoretical maximum value. On the other hand, fluorescence lifetime was greatly reduced to 0.27 ns (from 2.17 ns for the same fluorophores without nanostructure). This novel platform can be a promising utility for optical imaging and labeling of biological systems with a great sensitivity.

Gold Nanoparticles-enabled Efficient Dual Delivery of Anticancer Therapeutics to HeLa Cells

Colloidal gold nanoparticles (AuNPs) are of interest as non-toxic carriers for drug delivery owing to their advanced properties, such as extensive surface-to-volume ratio and possibilities for tailoring their charge, hydrophilicity and functionality through surface chemistries. To date, various biocompatible polymers have been used for surface decoration of AuNPs to enhance their stability, payloads capacity and cellular uptake. This study describes a facile one-step method to synthesize stable AuNPs loaded with combination of two anticancer therapeutics, -bleomycin and doxorubicin. Anticancer activities, cytotoxicity, uptake and intracellular localization of the AuNPs were demonstrated in HeLa cells. We show that the therapeutic efficacy of the nanohybrid drug was strongly enhanced by the active targeting by the nanoscale delivery system to HeLa cells with a significant decrease of the half-maximal effective drug concentration, through blockage of HeLa cancer cell cycle. These results provide rationale for further progress of AuNPs-assisted combination chemotherapy using two drugs at optimized effective concentrations which act via different mechanisms thus decreasing possibilities of development of the cancer drug resistance, reduction of systemic drug toxicity and improvement of outcomes of chemotherapy.

Colloidal ZnO nanoparticles for nonlinear optical probes and selective cell destruction

ZnO nanoparticles are notoriously difficult to use as optical probes due to the energy required for excitation. Nonlinear properties give a way around the high energy necessary for excitation. By using second harmonic generation, SHG, and multiphoton excitation, MPE, it is possible to use NIR light to generate intense coherent light that does not lead to heating of the cell or noncoherent light that also leads to sudden heating of the cell and cell destruction.

Self-assembled oligonucleotide semiconductor conjugated to GaN nanostructures for biophotonic applications

We investigate the optical properties of a new class of wide-bandgap semiconductor based biomaterial system. We have synthesized a guanosine derivative with a strong dipole moment, which self-assemble in ∼ 50 –100 nm confined pits to form a ribbon like semiconductor structure (SAGC). SAGC were successfully self-assembled on GaN/AlN QD matrix and the luminescence from GaN QDs can be resonantly transferred to the SAGC molecules resulting in a significant enhancement in emission from the guanine molecules. We also propose the design of ultraviolet-visible photonic bandgap structures based on hybrid SAGC-GaN photonic crystal.