Maria Gorbunova

The possibility of colorimetric determination of catecholamines using silica nanodots with a digital camera and smartphone is demonstrated. A lamp and a diode with emission wavelengths of 395 and 360 nm, respectively, are used as excitation sources. Color coordinates in the RGB, CMYK, and Lab systems, as well as some combinations thereof, are used as analytical signals. It is demonstrated that using a lamp as a source of ultraviolet radiation allows for achieving the best detection limits for all three catecholamines: 7, 0.1, and 1 μM when using a camera, and 12, 0.3, and 5 μM for dopamine, norepinephrine, and epinephrine, respectively, when using a smartphone. The data are obtained for the Euclidean distance analytical signal in the CMYK system. Using a camera and other color coordinate combinations as analytical signals can reduce the detection limits to 0.1 μM for epinephrine (coordinate combination L-a + b) and to 1 μM for dopamine (coordinate combination R + G + B). The pharmaceuticals “Dopamine-Ferein” (ZAO “Bryntsalov-A,” Russia), “Adrenaline Hydrochloride—Vial” (VIAL, China), and “Noradrenaline” (ZAO “EcoPharmPlus,” Russia) are analyzed. The results of colorimetric determination are in good agreement with the luminescence and HPLC analysis data.

A possibility of the luminescence determination of rutin with gold nanoclusters is shown. The approach is based on the luminescence quenching of the nanoclusters by rutin molecules, which occurs when the rutin absorption wavelengths overlap with wavelengths of the nanocluster excitation. The optimal conditions include pH 11–11.5 and ethanol concentration in the reaction mixture 20%; the time after mixing the reagents does not affect the result. Rutin can also be determined by spectrophotometry, and a combination of spectrophotometric and fluorometric signals increases analytical sensitivity. The limits of detection for rutin are 1.6 μM by fluorometry, 0.5 μM by spectrophotometry, and 0.3 μM using a combination of both techniques. The corresponding linear ranges are 4.8–100, 1.5–100, and 0.9–100 μM, respectively. Common inorganic ions, even in concentrations 100 times higher than that of rutin, do not interfere with the determination. The proposed procedure was successfully applied to an analysis of a biologically active supplement.

The study demonstrates that the interaction of dopamine with fluorescamine can serve as a basis for a fluorescence assay for dopamine using a camera, as the product formed in this interaction exhibits a fluorescence peak in the visible spectral region (485 nm). Fluorescence can be excited with a light-emitting diode emitting in the near-ultraviolet spectral region (395 nm). The reaction should be carried out at pH 8–8.5 in a phosphate buffer solution for 5 min, with fluorescamine being added to the reaction mixture last. The performance characteristics of the camera-based assay were evaluated and compared with those of a similar dopamine assay using a professional spectrofluorometer and a spectrophotometer. The limits of detection for dopamine using a camera, a spectrophotometer, and a spectrofluorometer were 1.8, 1.6, and 0.5 µM, respectively, while the analytical ranges were 5.4–50, 4.8–100, and 1.5–100 µM. The presence of common inorganic ions in concentrations 10 times higher than that of dopamine does not interfere with the assay. The proposed method for dopamine determination can be used for the quality control of pharmaceutical products.

A possibility of using a monitor calibrator for the determination of luminescent compounds is shown on an example of quinine. The determination is based on the irradiation of a sample with broadband radiation in the visible and near UV spectral regions from a built-in source exciting phosphor molecules and the simultaneous registration of the radiation incident on the detector. Measurement conditions are selected. Quinine can be determined in the range of 60−750 µM, the limit of detection is 20 µM. The determination is not affected by common inorganic ions, as well as sweeteners and acidity regulators present in many beverages. The developed method of determination is applicable to the analysis of carbonated drinks and drugs. Compared to a traditional spectrofluorimeter, monitor calibrator is characterized by compactness, mobility, ability of detecting luminescence in cuvettes of various sizes and shapes, and lower cost.

A monitor calibrator has been tested as a portable, available and cost-effective tool for detection of luminescence. Prospects of this device as an all-sufficient analogue of an analytical fluorometer have been outlined. Its ability to determine luminescent compounds was demonstrated by the example of rhodamine 3B and fluorescein. The determination is based on simultaneous impulse irradiation of a fluorescent sample with the incorporated continuous-spectrum light emitter in the visible and near UV ranges and registration of the luminescence. The appropriate cuvettes for the analysis and the device sealing film were chosen. The lowest relative detection limit for the developed approach was 0.03 μmol L-1 for rhodamine 3B and 0.01 μmol L-1 for fluorescein; the lowest absolute detection limits were 0.01 and 0.002 nmol for rhodamine 3B and fluorescein respectively. Using the proposed approach, it was possible to determine the luminescent compounds in tap water.

Capability of gold nanorods and their nanocomposites based on polyurethane foam as spectrophotometric reagents for catecholamines determination was examined. Comparison of the analytical properties of the systems based on interaction of nanoparticles of different morphology with various reagents in the presence of catecholamines was carried out, gold nanorods-based system is characterized by the highest sensitivity. Applicability of gold nanorods and their nanocomposites for catecholamines determination in biological fluids (urine, serum) was proved by HPLC analysis. Catecholamines preconcentration by dynamic sorption on hypercrosslinked polystyrene and further elution with 6M acetic acid could serve to improve the sensitivity of the analysis.

Results of studies on the analytical capabilities of gold nanoparticles in the methods of optical molecular absorption spectroscopy are reported. Peculiar effects of the nature of nanoparticle stabilizer, its charge, morphology of nanoparticles, form in which they are present in the system (in a colloidal solution or as a part of a nanocomposite with polyurethane foam) upon the determination of organic compounds (thiols, cationic compounds, catecholamines) and inorganic anions are considered. The determination is based on aggregation of nanoparticles or change in the state of their surface and morphology as a result of silver coating, leading to significant spectral and color changes, which can be monitored both by optical molecular absorption spectroscopy and visually. The ways to increase sensitivity and to control selectivity of the analysis using gold nanoparticles and their nanocomposites are outlined.