Field evidences of fluorescent dissolved organic matter (FDOM) as potential fingerprints for agricultural and urban sources in river environment.

Field evidences of the fluorescence differences between agricultural and urban river reaches are still lack. In this study, the middle reaches of Danhe River (DH) and Mihe River (MH) in Shouguang, China, were designed as agricultural and urban river reaches, respectively, to compare the the fluorescence differences in disparate river reaches using excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC). Three fluorescence components were identified. C1 (Ex/Em=230,255,295 nm/420 nm) was categorized as humic-like fluorophores, C2 (Ex/Em=230,275 nm/330 nm) was recognized as tryptophan-like substances, and C3 (Ex/Em=215 nm/290 nm) was noted as tyrosine-like and phenylalanine-like compounds. The results showed that the FDOM posed significant differences between agricultural and urban river reaches (P < 0.001). The monitoring sites in DH were rich in C2 (1.90 ± 0.62 Raman Unit (RU), mean ± standard deviation), and the monitoring sites in MH were rich in C3 (1.32 ± 0.51 RU). Redundancy analysis revealed that C2 could be regarded as a fluorescence indicator of agricultural sewage in river environment, while C3 was recognized as a fluorescence indicator of domestic sewage in river environment. In conclusion, this study provided field evidences of FDOM as potential fingerprints for agricultural and urban sources in river environment.

Step-Wise Assessment and Optimization of Sample Handling Recovery Yield for Nanoproteomic Analysis of 1000 Mammalian Cells.

Protein and peptide adhesion is a major factor contributing to sample loss during proteomic sample preparation workflows. Sample loss often has detrimental effects on the quality of proteomic analysis by compromising protein identification and data reproducibility. When starting with a low sample amount, only the most abundant proteins can be identified, which often offers little insights for biological research. Although the general idea about severe sample loss from low amount of starting material is widely presumed in the proteomics field, quantitative assessment on the impact of sample loss has been poorly investigated. In the present study, we have quantitatively assessed sample loss during each step of a conventional in-solution sample preparation workflow using bicinchoninic acid (BCA) and targeted LC/MS/MS protein and peptide assays. According to our assessment, for starting materials of ∼1000 mammalian cells, surface adhesion, along with desalting and speed-vacuum drying steps, all contribute heavily to sample loss, in particular for low-abundance proteins. With this knowledge, we have adapted slippery liquid infused porous surface (SLIPS) treatment, commercial LoBind tubes, and in-line desalting during sample processing. With these improvements, we were able to use a conventional in-solution sample handling method to identify on average 829 proteins with 1000 U2OS osteosarcoma cells (∼100 ng) with 75-min LC/MS/MS runs, an 11-fold increase in protein identification. Our optimized in-solution workflow is straightforward and also much less equipment- and technique-demanding than other advanced sample preparation protocols in the field.