1：Experimental Design and Method Selection:

A two-step gelation method was used, involving pre-gelation of sodium alginate with Ca2+ to form a gel template, followed by immersion in Cd(NO3)2 solution to form CdS QDs. This method was designed to constrain QD growth and avoid high temperatures.

2：Sample Selection and Data Sources:

Sodium alginate (SA) powder (Mn = 2.7×105) and various chemicals (e.g., CaCl2, Cd(NO3)2, Na2S) were purchased from specified suppliers. Ultrapure water was used for solution preparation.

3：7×105) and various chemicals (e.g., CaCl2, Cd(NO3)2, Na2S) were purchased from specified suppliers. Ultrapure water was used for solution preparation. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment includes SEM (Hitachi SU8010), TEM (JEOL JEM, 1011), HRTEM (JEOL JEM, 2100), XRD (PANalytical B.V. X’pert3), UV-vis spectrophotometer (Shimadzu UV-1800), PL spectrometer (HORIBA JOBIN YVON Fluoromax-4), luminescence spectrometer (Edinburgh Instruments FLS920), pH meter (Mettler-Toledo Sevenexcellence), zeta potential analyzer (Malvern Instruments Zetasizer Nano-ZS), FTIR spectrometer (Thermo Fisher Nicolet IS5), microplate reader (Tecan Spark), and MD simulation software (Material Studio 4.3 by Accelrys). Materials include SA, metal salts, Na2S, PBS, DMEM, FBS, MTT, etc.

4：3 by Accelrys). Materials include SA, metal salts, Na2S, PBS, DMEM, FBS, MTT, etc. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: SA-S solution was prepared by adding Na2S to SA solution. For the two-step method, SA-S drops were dripped into CaCl2 solution to form pre-gelled balls, which were then immersed in Cd(NO3)2 solution under nitrogen atmosphere at ambient temperature. The resulting gel balls were washed, dissolved in alkaline water for characterization, and purified by centrifugation and lyophilization. Various conditions (e.g., concentration, time, temperature) were explored.

5：Data Analysis Methods:

Morphology was analyzed via SEM, TEM, HRTEM; crystal structure via XRD; optical properties via UV-vis and PL spectroscopy; pH sensitivity via pH meter and FTIR; zeta potential via Malvern instrument; biocompatibility via MTT assay; stability via PL and zeta potential measurements over time; MD simulation for gelation process analysis.