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Total protein concentrations in the aqueous solutions were determined from the absorption spectra reproduced from smartphone-captured digital color images. We employed two different procedures for protein determination: the pyrogallol red molybdate method and Bradford's method. The principal-component-analysis-based reproduction process, which was previously reported by our research group, enabled the conversion of RGB values to score values for a linear combination of loading vectors to generate reproduced absorption spectra. The reproduced spectra were identical to those measured using a commercially available spectrophotometer. The total protein assays of commercial soymilk and human serum samples were carried out with both coloration reagents, and the obtained results were in good agreement with those attained using a conventional spectrophotometer. These results show that the proposed method enables smartphone-based ratiometric analysis of real samples without requiring any monochromating equipment.

The present dataset is related to the research paper entitled “Reproducing Absorption Spectra of pH Indicators from RGB Values of Microscopic Images” (Inagawa et al., 2020). The dataset contains microscopic images of aqueous methyl orange (MO), absorption spectra acquired with a spectrophotometer, loading spectra and calculation sheets for reproducing absorption spectra of aqueous MO from their RGB values of the microscopic images. The microscopic transmission images of the standard MO solutions at various pH conditions were acquired with a CMOS camera equipped with an invert microscope. Meanwhile, the loading spectra were obtained by principle component analysis of a series of absorption spectra of the standard solutions. The conversion matrix from RGB values in a region of interests (ROI) to score values were linear-algebraically determined from the RGB values and score values of the standard solutions. The absorption spectra of the sample solutions of which pH conditions are unknown were then reproduced by calculating the linear combination of the loading spectra with the score values obtained from the conversion process. Herein, the absorption spectra of MO are reproduced at various pH and ROI conditions.

Aggregation-induced emission (AIE) is a new technique for enhancing fluorescence. To demonstrate manipulation of near-infrared AIE by thermal stimuli for analytical use, we synthesized a thermoresponsive fluorescent polymer containing Au(I)–S bonds as near infrared fluorophores. We also examined the polymer for use as a fluorescent chemosensor based on the manipulation of AIE. The thermoresponsive fluorescent polymer was prepared from poly(N-isopropylacrylamide-co-methacrylic acid) by introducing thiol groups which were further modified to form fluorescent Au(I)–S bonds. The thermoresponsive fluorescent polymer aggregated and then fluoresced in the near infrared region due to AIE when heated above the phase transition temperature of 32 °C. The change in fluorescence intensity of the polymer was reversible by changing the solution temperature. Because the residual carboxyl groups make the thermoresponsive fluorescent polymer negatively ionizable, neutralization by the addition of positively charged analytes facilitates its aggregation to enhance fluorescence above the phase transition temperature. When hemoglobin, which has an isoelectric point of 6.8, was added to a pH 6.0 polymer solution at 40 °C, the polymer aggregated to enhance its fluorescence as a result of neutralization. A linear relationship between the hemoglobin concentration and the fluorescence intensity of the polymer was obtained for 0.5–2.0 g/L hemoglobin with a detection limit (3 s) of 0.014 g/L.

Simple and convenient preparation of metal nanoparticles has been a challenging issue to overcome in nano-technologies. To address this, spontaneous growth of gold nanoclusters to form gold nanoparticles in the presence of high molecular weight poly(ethylene glycol) (PEG) was studied under ambient conditions. Gold nanoclusters with a particle size of ∼2 nm spontaneously grew to form larger gold nanoparticles with a plasmonic absorption band at 520 nm only when in the presence of structurally organized PEG with a molecular weight of at least 2 × 106 g/mol, producing a pinkish colored solution. UV–vis absorption spectra indicate the existence of two steps responsible for gold nanocluster growth to form gold nanoparticles. The first step involves an increase in the absorbance of the spectral band at 520 nm during the first 10 min due to aggregation of gold nanoclusters. The second step is the broadening of this band at the same wavelength as a result of fusion followed by growth of the gold nanoclusters. Redox potentials and transmission electron microscopy (TEM) images reveal that structurally organized high molecular weight PEG induces aggregation of the gold nanoclusters and their subsequent growth to form larger nanoparticles, which exhibit plate-like triangular structures with sharp edges. Our study unveils the role that PEG plays in the growth process from gold nanoclusters to gold nanoparticles.

We propose a new principle for fabrication of size-tunable fluidic nano- and microchannels with a ubiquitous green material, water. Grooves filled with a solution are spontaneously formed on the surface of ice when an appropriate dopant is incorporated. Sucrose doping allows the development of grooves with lengths of 300 μm along the boundaries of ice crystal grains. This paper focuses on controlling the size of the liquid-filled groove and reveals its applicability to size-selective differentiation of nano- and micromaterials. The width of this groove can be varied in a range of 200 nm to 4 μm by adjusting the working temperature of the frozen platform. The channel dimension is reproducible as long as the same frozen condition is employed. We demonstrate the size-selective entrapment of particles as well as the state evaluation of DNA by controlling the physical interference of the ice wall with the electrophoretic migration of particles.