Human pepsin is a digestive protease
that plays an important role
in the human digestive system. The secondary structure of human pepsin
determines its bioactivity. Therefore, an in-depth understanding of
human pepsin secondary structure changes is particularly important
for the further improvement of the efficiency of human pepsin biological
function. However, the complexity and diversity of the human pepsin
secondary structure make its analysis difficult. Herein, a convenient
method has been developed to quickly detect the secondary structure
of human pepsin using a portable Raman spectrometer. According to
the change of surface-enhanced Raman spectroscopy (SERS) signal intensity
and activity of human pepsin at different pH values, we analyze the
change of the human pepsin secondary structure. The results show that
the content of the β-sheet gradually increased with the increase
in the pH in the active range, which is in good agreement with circular
dichroism (CD) measurements. The change of the secondary structure
improves the sensitivity of human pepsin SERS detection. Meanwhile,
human pepsin is a commonly used disease marker for the noninvasive
diagnosis of gastroesophageal reflux disease (GERD); the detection
limit of human pepsin we obtained is 2 μg/mL by the abovementioned
method. The real clinical detection scenario is also simulated by
spiking pepsin solution in saliva, and the standard recovery rate
is 80.7–92.3%. These results show the great prospect of our
method in studying the protein secondary structure and furthermore
promote the application of SERS in clinical diagnosis.
Organophosphorus (OPs) compounds have received enormous attention due to high neurotoxicity. However, the complex detection environment makes it very difficult to detect the OPs compounds at extremely low‐concentration. Therefore, it is vital to develop a high sensitive analytical method for the detection of low‐concentration OPs compounds at complex environment. Here, we proposed a novel surface‐enhanced Raman scattering (SERS) substrate based on the core‐shell structure Au@ZrO2 for the detection of extremely low‐concentration OPs compounds. By using above SERS substrate, we tested different kinds of OPs compounds and obtained excellent detection results. The detection limit of methyl parathion and triazophos can reach 0.01 mg/kg. Meanwhile, under the actual system (orange peel), the detection limit of the methyl parathion and triazophos also can reach 0.5 and 0.1 mg/kg, respectively. In addition, the above substrate is also very effective for the detection of dimethyl methylphosphonate (DMMP), a simulant for the chemical warfare agent (sarin), and the detection limit can reach 100 mg/kg. Besides, we also verified the reproducibility and stability of Au@ZrO2, which showed excellent properties. The relative standard deviation (RSD) of the SERS signal intensity for 20 tests was 6.38% and the enhancement ability of Au@ZrO2 can remain stable within 30 days. These results show that the proposed Au@ZrO2 SERS substrate has great potential in the detection of OPs compounds at extremely low‐concentration in the complex detection environment.
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