First, we have investigated the long-term stability of the produced Au NPs against agglomeration under ambient storage conditions. Figure Notably, Au10 possesses a higher tendency to agglomeration after about two months of storage, as indicated by the red-shift of the SPR peak by about 10 nm (inset of Figure ) and the larger hydrodynamic diameter (Fig. ). It should be noted that the K,NaPHI2 shows outstanding stability for at least two months, suggesting that K,Na-PHI is a remarkably effective stabilizer that endows the Au NPs with long-term stability. The increased tendency to the agglomeration of Au NPs at higher concentrations of KCya and KCA is most likely due to the shorter Debye-length of the electrical double layer as a consequence of the higher ionic strength.