Cacl2 dihydrate

Sodium alginate (NaAlg, viscosity: 15-25 cP) and calcium chloride (CaCl₂, dihydrate, purity ≥ 99.0%) were purchased from Sigma-Aldrich. Ta NPs (60 nm, 99.9% metals basis) were purchased from Aladdin Industrial Corporation. Iodixanol solution (commercial name Visipaque), a nonionic iodinated X-ray contrast agent, was purchased from GE Healthcare Company (Cork, Ireland). Dox was purchased from Zhejiang Hisun Pharmaceutical Co. Ltd. Milli-Q ultrapure water (18.2 MΩ) was used in all experiments. All chemicals were used as received without further purification.

HEK293A cells were transiently transfected with pcDNA3.1/puro-CAG plasmids expressing mGold or mVenus. Two days after transfection, the cells were washed with and imaged in extracellular solution. This solution contained 110 mM NaCl (catalog no. S3014, Sigma-Aldrich), 26 mM sucrose (catalog no. S0389, Sigma-Aldrich), 23 mM glucose (catalog no. G8270, Sigma-Aldrich), 5 mM KCl (catalog no. P9541, Sigma-Aldrich), 2.5 mM CaCl₂ dihydrate (catalog no. 223506, Sigma-Aldrich), and 1.3 mM MgSO₄ (catalog no. M2643, Sigma-Aldrich), and was adjusted to pH 7.4. Imaging was performed using the microscope described above (see the “Two-photon microscopy setup” section). Images were taken using various wavelengths from 700 to 1080 nm with 10 nm increments. The laser power was 10 mW for all wavelengths. Images were background corrected and manually segmented. The mean fluorescence of cells at each wavelength was calculated and plotted. We imaged at 900 nm with regular intervals during the spectral scanning and confirmed there was minimal photobleaching during the scanning. Small deviations in the actual power from the target power of 10 mW were corrected by assuming a quadratic dependence of fluorescence on illumination power.