We introduce a sensor molecule, AS140-MFC, consisting of a covalent adduct of an Ala-to-Cys mutant of alpha-synuclein with the 3-hydroxychromone dual emission dye MFC. We show that the AS140-MFC construct is a multiparametric fluorescent probe suitable for the continuous monitoring of protein aggregation and is sensitive to the early and intermediate stages of alpha-synuclein aggregation, a process associated with Parkinson's disease.

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3-Hydroxyflavone (3HF), a molecule that exhibits excited-state intramolecular proton transfer, has been studied for its fluorescence characteristics in dimyristoylphosphatidylcholine (DMPC) liposome membrane. 3HF partitions to the lipid bilayer membrane with a reasonably large partition coefficient. On excitation at 417 nm, a weak emission from the ground-state anion species was observed at 483 nm, whereas excitation at absorption maxima (345 nm) gives the usual intense fluorescence of the phototautomeric emission at 530 nm. In this article, we report the observation of a ground-state proton transfer reaction of 3HF in DMPC liposome membrane.

Surface-enhanced Raman scattering (SERS) is observed solitarily for analytes that are placed in the vicinity of plasmonic nanoparticles since the amplitude of the electric field on their surface decays with distance. Taking this idea forward, we have designed core−shell plasmonic systems for SERS sensing, consisting of silver nanoparticles coated with mesoporous silica (Ag@m-SiO 2 ) having an average pore size of 2.4 nm. Studies presented herein show that a Ag nanoparticle core of ∼55 nm and an m-SiO 2 shell of ∼40 nm represent a preferred combination for sieving and sensing, established by following the SERS of a standard marker, namely, rhodamine 6G. However, under identical conditions, Ag nanoparticles capped with microporous silica (Ag@SiO 2 ) inhibit the passage of analyte molecules into the plasmonic field. Yet another level of selectivity is provided by the negative surface charge of Ag@m-SiO 2 (ζ = −33 mV), eliminating negatively charged molecules from SERS sensing due to strong electrostatic repulsion. These aspects are confirmed using pyrene molecules, which are neutral, and pyrene derivatives carrying positive and negative charges. Thus, the SERS signal arises only from the neutral and positively charged molecules, which can penetrate into the pores, and not from the negatively charged analytes. The practical application of Ag@m-SiO 2 having a shell thickness of ∼40 nm for SERS sensing has been established using two commonly used organophosphorus pesticides (quinalphos and triazophos) directly from various vegetable matrices after the removal of plant pigments. The mesoporous silica shell of Ag@m-SiO 2 having a thickness of ∼40 nm sieves large molecules such as proteins and keeps them away from the electric field generated by the Ag nanoparticle, thus enabling the sensing of small molecules such as pesticides that penetrate into the shell.

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