785 nm diode laser

The Raman and SERS spectra were recorded using a Renishaw™ inVia Reflex Raman confocal multilaser spectrometer having a spectral resolution of 0.5 cm⁻¹. The wavelength calibration was performed using an internal silicon reference. All the spectra presented in this paper were acquired using a 100× (N.A = 0.85) objective. A 785 nm diode laser (Renishaw, UK) was used for excitation. The laser power (measured at the sample surface) was ~65 mW for Raman measurements and ~1.95 mW for SERS ones. The acquisition time was set to 10 s. The spectrograph was equipped with a 1200 lines/mm grating and a charge coupled device camera (CCD). WiRE 4.2 software (Renishaw plc, Gloucestershire, UK) was used for data collection and spectral pre-processing, including cosmic ray removal and baseline correction. The latter one was applied to all spectra in order to eliminate the fluorescence background. Each spectrum was an average of 30 spectral acquisitions from different positions of the whole dried sample area.

The Raman measurements were recorded using a confocal Renishaw^®inVia microscope (Renishaw plc, Wotton-under-Edge, UK), equipped with a Leica microscope (Leica Microsystems GmbH, Wetzlar, Germany), using a 100× objective (N.A. 0.85). A 785 nm diode laser (Renishaw, Wotton-under-Edge, UK) has been used for excitation. Prior to each set of measurements, a calibration procedure was performed using an internal silicon reference. The laser power (measured at the substrate surface) was ≈65 mW and the acquisition time was set between 3 and 10 s. The spectrograph was equipped with a 1200 lines/mm grating and a charge coupled device camera (CCD, Renishaw, Wotton-under-Edge, UK). The spectral resolution of the spectrometer was 0.5 cm⁻¹.
The SERS measurements performed on liquid solutions were recorded in 1 mL glass vials filled with 540 µL of colloid and 60 µL of analyte (methylene blue solutions of multiple concentrations) in the 200–2000 cm⁻¹ range, using a DeltaNu Advantage spectrometer (DeltaNu, Laramie, WY, USA) equipped with a laser diode emitting at 785 nm. The laser power was 100 mW and the spectral resolution was 5 cm⁻¹. Each SERS spectrum was the average of 10 recordings taken with an acquisition time of 10 s.

The Raman spectra were recorded using a Renishaw inVia Reflex Raman confocal multilaser spectrometer possessing a spectral resolution of 1 cm⁻¹. The wavelength calibration was performed using an internal silicon reference. All Raman spectra were acquired using a 50× (NA = 0.75) Leica objective. A 785 nm diode laser (Renishaw, Gloucestershire, UK) was used for excitation. The laser power (measured at the sample surface) was ~63 mW. The exposure time was set to 1 s, and 20 accumulations were used for each measurement.
The spectrograph was equipped with a 600 lines/mm grating and a charge-coupled device camera (CCD). WiRE 4.2 software (Renishaw plc, Gloucestershire, UK) was used for data collection and spectral preprocessing, including cosmic ray removal and baseline correction. The latter was applied to all spectra to eliminate the fluorescence background. Carbon dots spectrum represents an average of 25 spectral acquisitions from different positions of the whole dried ring sample area.