Vortex enrichment and detection of formaldehyde gas by urchin-shaped microspheres SERS sensor with omnidirectional detection enhancement effect

There is an immense potential for surface-enhanced Raman scattering (SERS) sensors in realizing the monitoring of poison gas. However, conventional SERS detection techniques are difficult to achieve omnidirectional detection, resulting in poor signals under large-angle laser excitation. Herein, urchin-shaped manganese dioxide (MnO 2 ) microspheres were grown directly in the flexible polyvinylidene fluoride (PVDF) cavity (PC) to obtain PC/MnO 2 (PCM). The PCM was modified by silver nanoparticles (Ag NPs) and zeolite imidazole framework-8 (ZIF-8) to form the PCM/Ag/ZIF-8 SERS sensor. In addition to enriching the target molecules and protecting the internal Ag NPs, ZIF-8 nanoparticles are able to modulate the distribution of “hot spots” on the spines of urchin-shaped MnO 2 . This modulation ensures the reliability of the PCM/Ag/ZIF-8 sensor by maintaining excellent SERS detection performance even under large-angle laser excitation. Furthermore, the unique urchin-shaped structure enables the gas to form vortex between neighboring spines, which greatly slows down the airflow and improves the contact time between the gas molecules and the sensor, thus achieving effective enrichment of the gas molecules. Experimental results show that the PCM/Ag/ZIF-8 sensor is capable of detecting formaldehyde gas at concentrations as low as 1 ppb. This work provides an innovative approach for reliable detection of toxic gases in practical applications.