2.3 ES-SMPS size characterization
The ES-SMPS system consisted of an aerosol generator (electrospray aerosol generator, ES; TSI 3480), a scanning mobility particle sizer (SMPS; TSI 3080) with a nano- differential mobility analyzer (DMA) column (TSI 3085), a condensed particle counter (CPC, TSI 3776). To generate droplets by the electrospray aerosol generator, the electrolyte with suitable conductivity is required and AmAc with a concentration of 20 mM has been recorded to produce droplets with the smallest size and the best performance. Therefore, AuNPs and proteins were suspended in 20 mM AmAc in this work. For NPs differentiation, the sheath flowrate was set as 20 L/min and aerosol flowrate was 1.5 L/min.