1：Experimental Design and Method Selection:

The study uses the nano-impact method (particle-electrode collision) for in-situ detection and sizing of silver nanoparticles (AgNPs) in real-world water samples. The method involves chronoamperometry at a carbon microdisc electrode held at 0.8 V vs. Ag/AgCl to oxidize impacting AgNPs, producing current spikes that are analyzed for charge transfer.

2：8 V vs. Ag/AgCl to oxidize impacting AgNPs, producing current spikes that are analyzed for charge transfer. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: AgNPs were synthesized in-house using a seeded growth method. Samples included suspensions of AgNPs in 20 mM KCl, bottled mineral water, kitchen tap water, and these waters with added citrate (2 mM). UV-vis spectroscopy was used for independent validation.

3：List of Experimental Equipment and Materials:

Equipment includes a homemade thermostat system with Peltier-effect heat pump, low-noise potentiostat, low-noise current amplifier (LCA-4K-1G, FEMTO Messtechnik GmbH), USB data acquisition device (USB-6003, National Instruments), carbon microdisc electrode (IJ Cambria Scientific Ltd), leakless Ag/AgCl reference electrode (eDAQ), platinum foil counter electrode (Goodfellow), UV-vis spectrophotometer (Shimadzu UV-1800), TEM (JEOL 3000F microscope). Materials include potassium chloride (Sigma-Aldrich), tri-sodium citrate (British Drug Houses), Evian bottled mineral water, tap water from University of Oxford, deionized water (Millipore), alumina powders (Buehler), carbon grids (Agar Scientific).

4：Experimental Procedures and Operational Workflow:

AgNPs were characterized by TEM for size determination. Nano-impact experiments were conducted in a Faraday cage with temperature control at 25.0 ± 0.1 °C. Chronoamperograms were recorded for 60 s in various media containing 12 pM AgNPs, with aging times from 0 to 70 min. Spikes were identified and analyzed using Python scripts. UV-vis measurements were performed over 60 min to monitor stability.

5：0 ± 1 °C. Chronoamperograms were recorded for 60 s in various media containing 12 pM AgNPs, with aging times from 0 to 70 min. Spikes were identified and analyzed using Python scripts. UV-vis measurements were performed over 60 min to monitor stability. Data Analysis Methods:

5. Data Analysis Methods: Spike charges were integrated and analyzed with diffusional weighting using Python scripts. TEM images were sized with Image J software. UV-vis data were used to track absorbance changes over time.