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Many applications of nano- and microparticles require molecular functionalization. Assessing the heterogeneity of a colloidal sample in terms of its molecular functionalization is highly desirable but not accessible by conventional ensemble experiments. Retrieving this information necessitates single-particle experiments which simultaneously detect both functionalized and nonfunctionalized particles via two separate imaging channels. In this contribution, we present an optical setup for performing correlative single-particle imaging using laser light-sheet illumination: the first detection channel records elastic light scattering (Rayleigh/Mie), while the second channel detects inelastic light scattering (Raman) or fluorescence. The instrument is tested with Raman reporter-functionalized SERS-active metal nanoparticles (core/satellite silver nanoparticles, dimers and monomers of gold nanoparticles) and fluorophore-functionalized colloids (fluorescent polymer microparticles, dye-labeled protein on gold nanoparticles).

An assay for Survivin, a small dimeric protein which functions as modulator of apoptosis and cell division and serves as a promising diagnostic biomarker for different types of cancer, is presented. The assay is based on switching on surface-enhanced Raman scattering (SERS) upon incubation of the Survivin protein dimer with Raman reporter-labeled gold nanoparticles (AuNP). Site-specificity is achieved by complexation of nickel-chelated N-nitrilo-triacetic acid (Ni-NTA) anchors on the particle surface by multiple histidines (His6-tag) attached to each C-terminus of the centrosymmetric protein dimer. Correlative single-particle analysis using light sheet laser microscopy enables the simultaneous observation of both elastic and inelastic light scattering from the same sample volume. Thereby, the SERS-inactive AuNP-protein monomers can be directly discriminated from the SERS-active AuNP-protein dimers/oligomers. This information, i.e. the percentage of SERS-active AuNP in colloidal suspension, is not accessible from conventional SERS experiments due to ensemble averaging. The presented correlative single-particle approach paves the way for quantitative site-specific SERS assays in which site-specific protein recognition by small chemical and in particular supramolecular ligands can be tested.

The kinetics of proteins passing through individual nuclear pore complexes (NPCs) of the nuclear envelope (NE) was studied using near-field scanning optical microscopy (NSOM) in combination with fluorescence correlation spectroscopy (FCS). The NSOM probe was placed over a single pore in an unsupported native NE to observe fluorescence-labeled NTF2 moving in the transport channel. A correlation analysis of the arising fluorescence fluctuations enabled us to characterize the translocation as driven by Brownian motion and to determine the related kinetic constants. Though trapped in the pore, NTF2 turned out to be highly mobile within a large axial extension. Our findings support the idea that molecules in transit interact with NPC proteins containing phenylalanine-glycine-repeat domains at the periphery of the channel. NSOM-FCS may help to understand the facilitated translocation in more detail and offers a new way to study single molecule mobility on a nanoscale.

The molecule of the title compound, C30H30S4, is located on a centre of inversion. The cyclopentene ring is almost planar. The thio­phene rings are twisted out of the plane of the cyclo­pentene ring by 47.41 (8) and 46.25 (9)°.

The cyclo­pentene ring of the title compound, C15H14Cl2S2, is almost planar. The two thio­phene rings are twisted out of the mean plane of the cyclo­pentene ring by 39.97 (5) and 50.84 (5)°.

Mol­ecules of the title compound, C8H7BrO2, are almost planar. The compound is isostructural with methyl 4-iodo­benzoate but not with methyl 4-chloro­benzoate. The crystal packing is characterized by a short Br⋯O inter­action of 3.047 (3) A.