Nir quest

The DRS equipment used in this study, illustrated in Figure 1, consisted of a broadband light source (HL-2000-HP, Ocean Optics, Edinburgh, United Kingdom) with emission ranging from 350 nm to 2400 nm, a quadrifurcated fiber optic probe with source-to-detector distance (SDD) of 630 µm (BF46LS01 1-to-4 Fan-Out Bundle, Thorlabs, Munich, Germany), a trifurcated fiber optic probe with SDD of 2500 µm (Fibertech Optica, Anjou, Canada), a visible/near-infrared (NIR) wavelength spectrometer (QE-Pro, Ocean Optics, Edinburgh, UK) and a NIR/SWIR spectrometer (NIR-Quest, Ocean Optics, Edinburgh, UK). The fiber optic probes were made of low-OH silica in order to allow better transmission at the SWIR range. These probes were used for both illumination and collection of the reflected light to be detected by the spectrometers. The visible/NIR spectrometer collected light in the wavelength range between 350 nm and 1140 nm, while the NIR/SWIR spectrometer detects light from 1090 nm to 1920 nm. The overlapping region was used to merge the spectra into one broadband spectrum from 350 nm to 1920 nm. Once reflected light was detected by the spectrometers, the intensity readings were preprocessed in order to obtain the tissue DRS spectra according to Section 2.5.

For large scale extinction spectra, a custom-built setup was used to simultaneously measure the visible (Ocean Optics QEPro from 300 nm to 1000 nm), near-infrared (Ocean Optics NIRQuest from 700 nm to 2000 nm), and mid-infrared (FTIR Interspec 402-X from 1700 nm to 20,000 nm) spectrum, using a thermal globar lamp source and ZnSe beam-splitters, and referenced to a clean gold mirror.

For spectral measurements the laser beam was directed into an integrating sphere (IC2, StellarNet, Inc.). The integrating sphere was fiber-coupled (QP600-1-SR-BX, Ocean Optics, Inc.) to a CCD-based spectrometer. For measurements in the range 200–1070 nm the HR2000 + (Ocean Optics, Inc.) spectrometer was used, and for measurements in the range 1070–1400 nm the NIRQuest (Ocean Optics, Inc.) spectrometer was used. The spectrum shown in Fig. 4 was joined together by matching the amplitude of the spectra obtained for the wavelength range around 1070 nm. All spectra are recorded over integration times significantly longer than the pulse period, and thus are averaged over a large number of pulses.

In this study, we constructed a DRS system consisting of a broadband light source (EQ-99X, Energetiq, USA), two spectrometers (QE65000 and NIR QUEST, Ocean Optics, USA), two 1 × 2 optical fiber switches (Piezosystem Jena, Germany), and a custom optical fiber probe as shown in Fig. 5. The fiber probe is harnessed with three aligned fibers of diameter and numerical aperture of 400 μm and 0.22, respectively, for light delivery and collection. A schematic of the fiber arrangement is shown in the inset of Fig. 5. A custom routine was developed to operate the system and record skin diffuse reflectance at the two source-to-detector separations (SDSs) within the wavelength range from 500 to 1600 nm for the determination of absorption and reduced scattering coefficients of skin.Figure 5

Schematic of the DRS system. Two optical switches were used in the system where one was used for switching light

source to one of the two source fibers, and the other was used to switch the collected light signal to one of the two spectrometers. The fiber setup of the optical probe is shown in the inset.

The spectral irradiance being absorbed by nanofluid is directly related to the photo-thermal conversion performance. The surfactant, ultrasonication time, and nanoparticle type can significantly impact the spectral irradiance being absorbed or transmitted through the nanofluid. The spectrophotometer (Ocean HDX, from Ocean Insight, USA) is used to measure the spectral irradiance ( $\mu$ W/cm²/nm) being transmitted through nanofluid in the mainly visible spectrum (400 – 800 nm). For the near-infrared region (900 – 2400 nm), the spectral irradiance transmitted was measured by spectrophotometer (NIR Quest, from Ocean Insight, USA). The halogen lamp (HL-2000-FHSA, from Ocean Insight, USA) was used as a light source during the experimentation.

A combination of optical spectrum analyzers are used to measure the UV–Vis–IR spectra. The spectrum in the range between 200 nm and 1100 nm is measured with a UV–Vis spectrometer (Ocean Optics HR 4000, 200–1100 nm), the range between 900 nm and 2500 nm with an NIR512 spectrometer ((Ocean Optics NIR quest, 900–2500 nm), and the range between 1000 nm and 5000 nm with an acousto-optic dispersive filter (MOZZA, Fastlite Inc. 1000–5000 nm). We calibrate the three collected spectra by interpolating the data and stitching them together in a shared region where these three spectrometers are reasonably effective. Using this methodology, we finally obtain the spectra displayed in Fig. 3.

The ssDNA-SWCNT complex suspension was diluted to 10 mg/L by 1× PBS before the fluorescence measurement. 5HT is the main substance used in terms of sensitivity, and DA, acetylcholine (Ach), GABA, Glu, UA, and AA were used to compare the fluorescence intensity to 5HT in terms of selectivity. Analytes were dissolved in DI water to make a stock solution, with concentrations of 1 mM DA, 5HT, Ach, GABA, Glu, AA, and 100 µM UA. Because of the low solubility of UA, 100 μM UA stock solution was used. 50 µL of each stock solution was added to 450 µL of sensor solution for a final analyte concentration of 100 µM except 10 µM for UA. 50 µL of DI water was added to the sensor solution for measuring baseline fluorescence. The fluorescence was measured after 20 min incubation and the change in the fluorescence spectrum was measured. A 721-nm laser (PSU-H-LED laser, CNI laser, Changchun, China) was used as an excitation light source, and detection was performed using an InGaAs photodiode array detector (NIRQuest, Ocean Insight, Orlando, FL, USA). Fluorescence measurements were performed in triplicate, and the average value was calculated and used for data analysis.