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.

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.

Biodegradable Poly(trehalose) Nanoparticle for Preventing Amyloid Beta Aggregation and Related Neurotoxicity.

Trehalose is a disaccharide that is capable of inhibiting protein aggregation and activating cellular autophagy. It has been shown that a polymer or nanoparticle form, terminated with multiple trehalose units, can significantly enhance the anti-amyloidogenic performance and is suitable for the treatment of neurodegenerative diseases. Here, we report a trehalose-conjugated polycarbonate-co-lactide polymer and formulation of its nanoparticles having multiple numbers of trehalose exposed on the surface. The resultant poly(trehalose) nanoparticle inhibits the aggregation of amyloid beta peptides and disintegrates matured amyloid fibrils into smaller fragments. Moreover, the poly(trehalose) nanoparticle lowers extracellular amyloid ß oligomer-driven cellular stress and enhances cell viability. The presence of biodegradable polycarbonate components in the poly(trehalose) nanoparticle would enhance their application potential as an anti-amyloidogenic material.

Enhanced Piezocatalysis by Calcium Phosphate Nanowires via Gold Nanoparticle Conjugation.

Piezocatalytic materials have considerable application potential in wireless therapy. Most of these applications require biocompatible nanomaterials for in vivo targeting and control of intracellular processes. However, the piezocatalytic performance of a material decreases at a nanometer size regime, and most of the biocompatible materials have poor piezocatalytic efficiency. In particular, hydroxyapatite or calcium phosphate-based nanomaterials have weak piezocatalytic properties that limit the biomedical application potential. Here, we show that anisotropic shape and Au nanoparticle conjugation can enhance the piezocatalytic property of a calcium phosphate nanomaterial by 10 times and the performance approaches that of the bulk/nanoparticle form of well-known BaTiO3. The colloidal form of calcium phosphate nanowires/nanorods/nanospheres (2-5 nm diameter and 30-1000 nm length) and their Au nanoparticle (5-8 nm) composites are prepared, and their piezoelectric properties have been investigated with piezoresponse force microscopy. It has been observed that the anisotropic nanowire structure of calcium phosphate can enhance the piezoelectric property by 2 times and Au nanoparticle conjugation can enhance it up to 10 times with a piezoelectric constant value of 72 pm/V, which is close to the value of the bulk/nanoparticle form of BaTiO3. This enhanced piezoelectric property is shown to enhance the piezocatalytic reactions by 10 times. The approach has been used to design colloidal nano-bioconjugate for selective labeling of cancer cells, followed by wireless cell therapy via medical-grade ultrasound-based intracellular reactive oxygen species generation. The developed approach and material can be extended for wireless therapeutic applications and for controlling intracellular processes.