Blinking Carbon Dots as a Super-resolution Imaging Probe.

Single-molecule localization microscopy (SMLM) emerges as a powerful approach for super-resolution imaging that provides unprecedented resolution at the nanometer length scale. However, the development of appropriate probes with specific photophysical traits and characteristics is crucial for this approach. This study demonstrates two different fluorescent carbon dots (CDs) derived from the same molecular precursor─one emitting in red and the other in green─as a SMLM-based super-resolution imaging probe for different applications with an average localization precision of 20 nm and a resolution of 60 nm. Both the CDs exhibit spontaneous blinking with high photon count and low duty cycle but with different blinking cycles. The red emissive CDs with a lower blinking cycle are ideal for quantitative analysis, whereas green emissive CDs with a higher blinking cycle are ideal for high-resolution imaging. We show that the difference in blinking features is linked to their chemical compositions, and the presence of much denser trap states in red emitting CDs is responsible for the reduction of its blinking cycle. This study shows that CDs can be designed as a potential probe for SMLM-based super-resolution imaging for diverse bioimaging applications.

Arginine Surface Density of Nanoparticles Controls Nonendocytic Cell Uptake and Autophagy Induction.

Nonendocytic cell uptake of nanomaterials is challenging, which requires specific surface chemistry and smaller particle size. Earlier works have shown that an arginine-terminated nanoparticle of <10-20 nm size shows nonendocytic uptake via direct membrane penetration. However, the roles of surface arginine density and the arginine-arginine distance at the nanoparticle surface in controlling such nonendocytic uptake mechanism is not yet explored. Here we show that a higher arginine density at the nanoparticle surface with an arginine-arginine distance of <3 nm is the most critical aspect for such nonendocytic uptake. We have used quantum dot (QD)-based nanoparticles as a model for fluorescent tracking inside cells and for quantitative estimation of cellular uptake. We found that arginine-terminated nanoparticles of 10 nm size can opt for the energy-dependent endocytosis pathway if the arginine-arginine distance is >3 nm. In contrast, nanoparticles with <3 nm arginine-arginine distance rapidly enter into the cell via the nonendocytic approach, are freely available in the cytosol in large amounts to capture the cellular adenosine triphosphate (ATP), generate oxidative stress, and induce ATP-deficient cellular autophagy. This work shows that arginine-arginine distance at the nanoparticle surface is another fundamental parameter, along with the particle size, for the nonendocytic cell uptake of foreign materials and to control intracellular activity. This approach may be utilized in designing nanoprobes and nanocarriers with more efficient biomedical performances.

Piezoelectric Amyloid Fibril for Energy Harvesting, Reactive Oxygen Species Generation, and Wireless Cell Therapy.

Biomolecular piezoelectric materials are envisioned for advanced biomedical applications for their robust piezoelectricity, biocompatibility, and flexibility. Here, we report the piezoelectric property of amyloid fibrils derived from three distinct proteins: lysozyme, insulin, and amyloid-ß. We found that piezoelectric properties are dependent on the extent of the ß-sheet structure and the extent of fibril anisotropy. We have observed the piezoelectric constant value in the range of 24-42 pm/V for fibrils made of lysozyme/insulin/amyloid-ß, and for the sheet/bundle-like structure of lysozyme aggregates, the value becomes 62 pm/V. These piezoelectric constant values are 4-10 times higher than the native lysozyme/insulin/amyloid proteins. Computational studies show that extension of the ß-sheet structure produces an asymmetric arrangement of charges (in creating dipole moment) and mechanical stress induces an aligned orientation of these dipoles that results in a piezoelectric effect. It is shown that these piezoelectric fibrils can harvest mechanical as well as ultrasound-based energy to produce a voltage of up to 1 V and a current of up to 13 nA. These fibrils are employed for reactive oxygen species (ROS) generation under ultrasound exposure and utilized for ultrasonic degradation of organic pollutants or killing of cancer cells via intracellular ROS generation under ultrasound exposure. Our findings demonstrate that the piezoelectric property of protein fibrils has potential for wireless therapeutic applications and may have physiological roles that are yet to be explored.

Ultrasonic Electroporation for Cells Grown on Piezoelectric Film Composed of Hydroxyapatite Nanowire and PVDF.

The delivery of cell impermeable exogenous material into live cells by external stimuli is critical for both biological research and therapeutic applications. Although electroporation-based delivery of foreign materials inside the cell is a powerful approach, cell viability is often compromised due to the requirement of high voltage. Here, we report a piezoelectric hydroxyapatite nanowire-embedded poly(vinylidene fluoride) (PVDF) film for ultrasonic electroporation-based delivery of foreign materials to adherent cells. We found that 9 wt % loading of hydroxyapatite nanowires into PVDF can enhance the piezoelectric property by 2-3 times (with a piezoelectric constant value of 58 pm/V) than pure PVDF/nanowire, which is comparable to commonly known piezoelectric ceramics. These films can harvest mechanical as well as ultrasound-based energy to produce electrical potential up to 2 V. This biocompatible film can be used to grow cells on top of it and for subsequent application of ultrasound to exert electric voltage on cell membrane. We found that ultrasonic exposure to adhered cells leads to reversible pore formation on cell membrane that offers intracellular delivery of FITC-dextran with 75% efficiency. The developed piezoelectric film-based ultrasonic electroporation can be used for wireless electroporation in remote areas.

Modulatory role of copper on hIAPP aggregation and toxicity in presence of insulin.

Aggregation of the human islets amyloid polypeptide, or hIAPP, is linked to ß-cell death in type II diabetes mellitus (T2DM). Different pancreatic ß-cell environmental variables such as pH, insulin and metal ions play a key role in controlling the hIAPP aggregation. Since insulin and hIAPP are co-secreted, it is known from numerous studies that insulin suppresses hIAPP fibrillation by preventing the initial dimerization process. On the other hand, zinc and copper each have an inhibitory impact on hIAPP fibrillation, but copper promotes the production of toxic oligomers. Interestingly, the insulin oligomeric equilibrium is controlled by the concentration of zinc ions when the effect of insulin and zinc has been tested together. Lower zinc concentrations cause the equilibrium to shift towards the monomer and dimer states of insulin, which bind to monomeric hIAPP and stop it from developing into a fibril. On the other hand, the combined effects of copper and insulin have not yet been studied. In this study, we have demonstrated how the presence of copper affects hIAPP aggregation and the toxicity of the resultant conformers with or without insulin. For this purpose, we have used a set of biophysical techniques, including NMR, fluorescence, CD etc., in combination with AFM and cell cytotoxicity assay. In the presence and/or absence of insulin, copper induces hIAPP to form structurally distinct stable toxic oligomers, deterring the fibrillation process. More specifically, the oligomers generated in the presence of insulin have slightly higher toxicity than those formed in the absence of insulin. This research will increase our understanding of the combined modulatory effect of two ß-cell environmental factors on hIAPP aggregation.

Naringenin-Functionalized Gold Nanoparticles and Their Role in α-Synuclein Stabilization.

Misfolding and self-assembly of several intrinsically disordered proteins into ordered ß-sheet-rich amyloid aggregates emerged as hallmarks of several neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Here we show how the naringenin-embedded nanostructure effectively retards aggregation and fibril formation of α-synuclein, which is strongly associated with the pathology of Parkinson's-like diseases. Naringenin is a polyphenolic compound from a plant source, and in our current investigation, we reported the one-pot synthesis of naringenin-coated spherical and monophasic gold nanoparticles (NAR-AuNPs) under optimized conditions. The average hydrodynamic diameter of the produced nanoparticle was ∼24 nm and showed a distinct absorption band at 533 nm. The zeta potential of the nanocomposite was ∼-22 mV and indicated the presence of naringenin on the surface of nanoparticles. Core-level XPS spectrum analysis showed prominent peaks at 84.02 and 87.68 eV, suggesting the zero oxidation state of metal in the nanostructure. Additionally, the peaks at 86.14 and 89.76 eV were due to the Au-O bond, induced by the hydroxyl groups of the naringenin molecule. The FT-IR analysis further confirmed strong interactions of the molecule with the gold nanosurface via the phenolic oxygen group. The composite surface was found to interact with monomeric α-synuclein and caused a red shift in the nanoparticle absorption band by ∼5 nm. The binding affinity of the composite nanostructure toward α-synuclein was in the micromolar range (Ka∼ 5.02 × 106 M-1) and may produce a protein corona over the gold nanosurface. A circular dichroism study showed that the nanocomposite can arrest the conformational fluctuation of the protein and hindered its transformation into a compact cross-ß-sheet conformation, a prerequisite for amyloid fibril formation. Furthermore, it was found that naringenin and its nanocomplex did not perturb the viability of neuronal cells. It thus appeared that engineering of the nanosurface with naringenin could be an alternative strategy in developing treatment approaches for Parkinson's and other diseases linked to protein conformation.

Loop Dynamics and Conformational Flexibility in Dengue Serine Protease Activity: Noninvasive Perturbation by Solvent Exchange.

Molecular mechanics play an important role in enzyme action and understanding the dynamics of loop motion is key for designing inhibitors of an enzyme, particularly targeting the allosteric sites. For the successful creation of new protease inhibitors targeting the dengue serine protease, our current investigation detailed the intricate structural dynamics of NS2B/NS3 dengue protease. This enzyme is one of the most essential enzymes in the life cycle of the dengue virus, which is responsible for the activation/processing of viral polyprotein, thus making it a potential target for drug discovery. We showed that the internal dynamics of two regions, fingers 1 and 2 (R24-G39 and L149-A164, respectively) adjacent to the active site triad of this protease, control the enzyme action. Each of these regions is composed of two antiparallel ß-strands connected by ß-turn/hairpin loops. The correlated bending and rocking motions in the two ß-turns on either side of the active site were found to modulate the activity of the enzyme to a large extent. With increasing concentration of cosolvent dimethyl sulfoxide, correlated motions in the finger 2 region get diminished and bending of finger 1 increases, which are also reflected in the loss of enzyme activity. Decreasing temperature and mutations in neighboring nonsubstrate binding residues show similar effects on loop motion and enzyme kinetics. Therefore, in vitro noninvasive perturbation of these motions by the solvent exchange as well as cold stress in combination with in silico molecular dynamics simulations established the importance of the two ß-turns in the functioning of dengue virus serotype 2 NS2B/NS3 serine protease.

Crossover of positive and negative magnetoconductance in composites of nanosilica glass containing dual transition metal oxides.

A facile sol-gel approach to prepare composites of nanosilica glass containing dual transition metal oxides with compositions xCoO·(20 - x)NiO·80SiO2 comprising x values 5 (NC-1), 10 (NC-2) and 15 (NC-3) within hexagonal pores of SBA-15 template has been demonstrated. The synergistic effect of dual transition metal oxide ions on MD properties and crossover of positive and negative magnetoconductance phenomena were observed in these nanocomposite systems. The physical origin of magnetoconductance switching is explained based on the factors: nanoconfinement effect, wave-function shrinkage and spin polarized electron hopping. DFT calculations were performed to understand the structural correlation of the nanoconfined system. The static (dc) and dynamic (ac) responses of magnetization revealed the spin-glass behaviour of the investigated samples. Both scaling law and Vogel-Fulcher law provide a satisfactory fit to our experimental results which are considered as a salient feature of the spin-glass system. Our studies indicate the possibilities of fabricating magnetically controlled multifunctional devices.

Giant Dielectric Constant of Copper Nanowires/Amorphous SiO2 Composite Thin Films for Supercapacitor Application.

Transparent thin films comprising ultralong (within the range 52-387 µm) copper nanowires with diameter ∼7-9 nm encapsulated in amorphous silica have been successfully fabricated using an electrodeposition technique. The length and number density were controlled by electrodeposition time and concentration of precursor materials, respectively. Giant dielectric constant values (∼1010) obtained from these systems were quantitatively explained as a function of the length of the nanowires on the basis of quantum mechanical theory derived by Rice and Bernasconi. These transparent thin films offer a specific capacitance value of 550 F/g with more than 73% cyclic stability over a period of 900 cycles. Our findings demonstrate a facile pathway to control and improve the properties of metal nanowire-based transparent materials for use in supercapacitor applications.

Reactional state in lepromatous leprosy simulating Sweet's syndrome.

Erythema nodosum leprosum (ENL) or Type-2 lepra reaction is a manifestation of type-III hypersensitivity response, and usually occurs in certain cases of lepromatous and borderline lepromatous leprosy. ENL may present as widespread crops of erythematous, inflamed nodules and papules. Rare variants of ENL mimicking pemphigus or Sweet's syndrome (SS) have been documented. Here, we report an unusual case of persistent ENL in a 52-year-old lady, which we could diagnose with the help of skin biopsy and histopathological examination.

Acute acalculus cholecystitis in dengue fever.

Atypical manifestations of dengue fever (DF) and dengue haemorrhagic fever (DHF) involving different organs are being increasingly recognised, especially in the dengue endemic areas. We report an atypical presentation of DF in a 22 year old lady presenting with fever and acute pain in the right hypochondrium, diagnosed to be acute acalculus cholecystitis (AAC).

Atypical central nervous system involvement in acute organophosphorous poisoning.

Extrapyramidal syndrome is an uncommon sequelae of acute organophosphorous (OP) poisoning. It is a manifestation of the intermediate syndrome described in OP poisoning. It may or may not be associated with neuroimaging changes in the striatum. We present a case of acute OP poisoning with interesting positive CT scan findings.