Fluoromax spectrofluorometer

Fluorescence excitation/emission spectra were measured in a quartz cuvette using the FluoroMax+ spectrofluorometer (Horiba Scientific, Kisshoin Minami-Ku Kyoto, Japan).

Milli-Q water was used in the case of AltMV VLPs and SP_VLP, 15 mM NaCl solution was used for SP_V and 12.5 mM Tris-HCl pH 8.0 was used in the case of AltMV virions for far-UV CD and intrinsic fluorescence measurements. CD spectra in the 200–260 nm region were recorded in 1–2 mm cells at 25°C, using a Chiroscan CD spectrometer (Applied Photophysics, Surrey, UK). Sample concentrations were in the range of 0.1–0.3 mg/ml. The spectra were recorded at a speed of 0.5–1.0 nm/s with baseline subtraction. The spectra measured were smoothed using the instrument software Pro Data. The [ϴ] values were calculated taking the mean molecular weight of amino acid residues to be 110. The intrinsic fluorescence spectra were recorded in 1 cm cells, using a FluoroMax spectrofluorometer (HORIBA Jobin Yvon, Edison, NJ, USA), at 25°C. Fluorescence was excited at 280 nm and the emission spectra were recorded in the 300–400 nm range.

Steady-state excitation and emission spectra were recorded on a FluoroMax spectrofluorometer (Horiba Instruments Inc., U.S.A.) using quartz cuvettes with either a 5 mm or a 10 mm path length. Tryptophan was excited at 295 nm to minimize tyrosine excitation. Three scans were recorded and averaged.

Photoluminescence spectra of aqueous dispersions of C-dots were recorded using a Horiba Fluoromax spectrofluorometer at excitation wavelengths (λ_ex) between 320 and 500 nm. The QY was determined via the equation: $$\mathrm{QY}={\mathrm{QY}}_{\mathrm{R}}\times \left(\frac{\mathrm{I}}{{\mathrm{I}}_{\mathrm{R}}}\right)\times \left(\frac{{\mathrm{A}}_{\mathrm{R}}}{A}\right)\times \left(\frac{{\mathrm{\eta }}^2}{{\mathrm{\eta }}_{\mathrm{R}}^2}\right)$$ where, I, A, and η denote the integrated fluorescence intensity, absorbance, and the refractive index, respectively. The subscript R indicates the reference dye anthracene that was dissolved in ethanol giving QY_R = 0.27 at λ_ex = 365 nm. The error bars have been calculated based on a series of three independently repeated experiments.

Horiba-Fluoromax Spectrofluorometer is employed for all fluorescence measurements. The competitive dye displacement assay is done to unravel the binding mode of the CMT-AgNPs–ctDNA complex^{31 (link)}. The DNA binding dyes Hst and MetG were used for the assay as it has an intense fluorescence intensity due to their known minor and major groove mode of binding with DNA respectively^{32 (link),33 (link)}. Thus, the nature of interaction or binding could be easily identified by tracking the modifications in fluorescence intensities of the dye–DNA complex by adding CMT-AgNPs.