Table 1.

Troubleshooting table

Step	Problem	Possible reason	Solution
1A	Nanoparticle size is smaller or larger than 60 nm	The gold chloride:citrate ratio is smaller or larger, respectively, than 10:1	Make sure the concentration of the stock solution are correct or prepare fresh stock solutions.
1B	Dispersion slowly changes from blue to pink	Residual reagents are present in the dispersion	Dialyze the collected nanoparticles against DI water and keep the dispersion ice-cold.
6	Dark purple color appears	Gold nanoparticle aggregation due to high ionic strength	Lower dye concentration or dialyze the gold nanoparticles longer
22A	Silica shell too thin	Ammonium hydroxide or water concentration too low	Use fresh ammonium hydroxide or add more water during step 4–6
22A	Free silica	Reaction time too long or reaction was not sufficiently quenched	Quench the reaction at 15 min reaction time with sufficient amounts of ethanol
22D	Fluorescent interference	Residual resonant Raman reporter	Wash SERRS nanoparticles thoroughly
23B	Difficult to inject	SERRS nanoparticle agglomeration	Sonicate the dispersion right before injection