Fluorescence enhanced microfluidic sensor with CsPbI3 probe for lubricant copper ions on-site rapid detection based on SiO2 inverse opal photonic crystals

Cu2+ content in diesel engine lubricating oil refers to a vital parameter suggesting the quality of oil and judging mechanical wear. Accordingly, the on-site rapid copper ions content determination in lubricant is of great sig-nificance to safe operation of diesel engines. However, most of the current researches on detection are carried out in laboratory, requiring the use of large-scale equipment such as spectrometer, which are not suitable for rapid on-site detection. Quantum dot-based optical microfluidic chip provides the possibility for heavy metal ions on-site detection, but it is subject to the defect of weak fluorescence intensity, thereby the increase in sensitivity is limited. In the present study, a microfluidic sensor using SiO2 inverse opal photonic crystals (IOPCs) to heighten CsPbI3 perovskite quantum dots (PQDs) photoluminescence (PL) intensity is proposed, which can realize rapid Cu2+ content detection in lubricant. Firstly, the selective detection characteristic of CsPbI3 on Cu2+ was studied. Experimental results showed that the photoluminescence of CsPbI3 was significantly quenched by Cu2+ because electrons were effectively transferred from CsPbI3 to Cu2+. Subsequently, to enhance the fluorescence intensity of CsPbI3 probe, the SiO2 IOPCs structure was formed in chip detection well. The effective PL intensity of CsPbI3 PQDs was enhanced by the photonic stopband effect formed by the periodically arranged micro-nano structure of photonic crystals. This enhancement effect was attributed to the coupling effect between stopband with exci-tation and emission light. As the stopband of SiO2 IOPCs was coupled with the excitation light wavelength and emission light wavelength of CsPbI3, the enhancement factors could reach 17-fold and 22-fold, respectively. The mentioned strategy could effectively improve the detection sensitivity of the microfluidic sensor and reduce the detection limit to 0.34 nM. Moreover, the formed microfluidic sensor system can be used for determination of Cu2+ content in lubricating oil on site. Meanwhile, the sturdy porous structure of SiO2 IOPCs also facilitated target metal ions to be captured and enriched.

Automated summary

This study introduces a microfluidic sensor using SiO2 inverse opal photonic crystals to enhance CsPbI3 perovskite quantum dots photoluminescence intensity, allowing for rapid detection of Cu2+ content in lubricant. By studying the selective detection characteristic of CsPbI3 on Cu2+ and forming the SiO2 IOPCs structure in chip detection well, the detection sensitivity was effectively improved, reducing the detection limit to 0.34 nM.