Amino acids

Amino acids were purchased or synthesized from Bachem, Macklin, Energy Chemical, J&K Scientific, GL Biochem (Shanghai) Ltd., or Aladdin Biochemical Technology Co. Ltd. Proteinase K from Tritirachium album, pepsin from porcine gastric mucosa, and pancreatin from porcine pancreas were purchased from Sigma-Aldrich. Hydrochloric acid (HCl), sodium hydroxide (NaOH), sodium chloride (NaCl), and monobasic potassium phosphate (KH₂PO₄) were products of Beijing Chemical Co. Ltd. The CQDs were purchased from Suzhou Xingshuo Nanotech Co. Ltd. The dyes Nile red, thioflavin T, rubrene, rhodamine B, and rhodamine 6G (R6G) were purchased from Sigma-Aldrich. CA was a product of Shanghai Yuanye Bio-Technology Co. Ltd. Composting soil was purchased from a local facility. Water was obtained from a double-stage Milli-Q Plus purification system (Millipore, America). All solutions were freshly prepared and filtered for immediate use.

General chemicals and reagents were purchased from Fisher Acros (Hampton, NH, USA). Isothiocyanobenzyl-NTA was purchased from Biomass (Rockville, MD, USA). Tentagel S NH₂ resin was purchased from RAPP polymer (Tuebingen, Germany). Dynabeads^TM MyOne^TM Streptavidin C1, Streptavidin-alkaline phosphatase (SAAP), and 5-bromo-4-chloro-3-indolyl-phosphate (BCIP) were obtained from Thermofisher (Hampton, NH, USA). Amino acids, coupling reagents, and biotin were purchased from GL-Biochem. BSA (Shanghai, China), lysozyme, and dipeptides were obtained from Sigma-Aldrich (St. Louis, MO, USA). Ni Sepharose 6 FastFlow beads were obtained from GE Healthcare (Chicago, IL, USA).
MALDI-TOF-MS and MALDI-TOF-MS/MS analysis were performed by a Bruker Micro-flex MALDI-TOF mass spectrometer (Billerica, MA, USA) and a Bruker Ultra-flextreme MALDI-TOF/TOF mass spectrometer. The HPLC analysis and HPLC purification were performed using Agilent 1260 Infinity (Agilent, Santa Clara, CA, USA). Positive bead (blue beads) screening was performed with a Nikon SMZ 745T microscope (Nikon, Tokyo, Japan).