The variation of particle size, size distribution, aggregation state, intensity-autocorrelation function and ξ potential of the nanocrystallites in urine of lithogenic patients and healthy subjects following the placement time were comparatively investigated by nanoparticle size analyzer and transmission electron microscopy(TEM). As the placement period increased from 0 h to 3 h, the average diameter(Da) increased from 506 nm to 958 nm. The size distribution of particles became much wider, the autocorrelation time increased from 1.84 s to 3.93 s, and the ξ potential was decreased from -1.34 mV to -3.89 mV. However, Da in healthy urine increased only from 330 nm to 416 nm, the autocorrelation time increased from 1.44 s to 2.10 s, and the ξ potential was decreased from -8.35 mV to -8.90 mV. When the above process was repeated after these two types of urine samples received the second ultrasound treatment, all properties of urinary nanocrystallites basically repeated the above variation rules. It indicated that the nanocrystallites in the urine of lithogenic patients not only was distinctly different from those of healthy patients in particle size, size distribution, aggregation state, intensity-autocorrelation function and ξ potential, etc., but also had lower stability; the nanocrystallites in lithogenic urine can gradually agglomerate with the prolongation of placement period. These results are explained from the concentration difference between inhibitors with large and small molecules in the two types of urine, the stability of electric double layer formed on the surface of urinary nanocrystallites, etc. The results show that the aggregation of urinary nanocrystallites is the key factor to stone placement.
