Characterization of Noise in a Single-Molecule Fluorescence Signal

Promising breakthroughs in amyotrophic lateral sclerosis treatment through nanotechnology's unexplored frontier

This review explores the transformative potential of nanotechnology in the treatment and diagnosis of amyotrophic lateral sclerosis (ALS), a progressive neurodegenerative disorder characterized by motor neuron degeneration, muscle weakness, and eventual paralysis. Nanotechnology offers innovative solutions across various domains, including targeted drug delivery, neuroprotection, gene therapy and editing, biomarker detection, advanced imaging techniques, and tissue engineering. By enhancing the precision and efficacy of therapeutic interventions, nanotechnology facilitates key advancements such as crossing the blood-brain barrier, targeting specific cell types, achieving sustained therapeutic release, and enabling combination therapies tailored to the complex pathophysiology of ALS. Despite its immense promise, the clinical translation of these approaches faces challenges, including potential cytotoxicity, biocompatibility, and regulatory compliance, which must be addressed through rigorous research and testing. This review emphasizes the application of nanotechnology in targeted drug delivery and gene therapy/editing for ALS, drawing on the author's prior work with various nanotechnological platforms to illustrate strategies for overcoming similar obstacles in drug and gene delivery. By bridging the gap between cutting-edge technology and clinical application, this article aims to highlight the vital role of nanotechnology in shaping the future of ALS treatment.

Dual-wavelength metalens enables Epi-fluorescence detection from single molecules

Single molecule fluorescence spectroscopy is at the heart of molecular biophysics research and the most sensitive biosensing assays. The growing demand for precision medicine and environmental monitoring requires the creation of miniaturized and portable sensing platforms. However, the need for highly sophisticated objective lenses has precluded the development of single molecule detection systems for truly portable devices. Here, we propose a dielectric metalens device of submicrometer thickness to excite and collect light from fluorescent molecules instead of an objective lens. The high numerical aperture, high focusing efficiency, and dual-wavelength operation of the metalens enable the implementation of fluorescence correlation spectroscopy with a single Alexa 647 molecule in the focal volume. Moreover, the metalens enables real-time monitoring of individual fluorescent nanoparticle transitions and identification of hydrodynamic diameters ranging from a few to hundreds of nanometers. This advancement in sensitivity extends the application of the metalens technology to ultracompact single-molecule sensors.

Tetrameric Antibody Complexes and Affinity Tag Peptides for the Selective Immobilization and Imaging of Single Quantum Dots

Colloidal semiconductor quantum dots (QDs) are of widespread interest as fluorescent labels for bioanalysis and imaging applications. Single-particle measurements have proven to be a very powerful tool for better understanding the fundamental properties and behaviors of QDs and their bioconjugates; however, a recurring challenge is the immobilization of QDs in a solution-like environment that minimizes interactions with a bulk surface. Immobilization strategies for QD-peptide conjugates are particularly underdeveloped within this context. Here, we present a novel strategy for the selective immobilization of single QD-peptide conjugates using a combination of tetrameric antibody complexes (TACs) and affinity tag peptides. A glass substrate is modified with an adsorbed layer of concanavalin A (ConA) that binds a subsequent layer of dextran that minimizes nonspecific binding. A TAC with anti-dextran and anti-affinity tag antibodies binds to the dextran-coated glass surface and to the affinity tag sequence of QD-peptide conjugates. The result is spontaneous and sequence-selective immobilization of single QDs without any chemical activation or cross-linking. Controlled immobilization of multiple colors of QDs is possible using multiple affinity tag sequences. Experiments confirmed that this approach positions the QD away from the bulk surface. The method supports real-time imaging of binding and dissociation, measurements of Förster resonance energy transfer (FRET), tracking of dye photobleaching, and detection of proteolytic activity. We anticipate that this immobilization strategy will be useful for studies of QD-associated photophysics, biomolecular interactions and processes, and digital assays.