Zinc oxide nanostructures for fluorescence and Raman signal enhancement: a review

Abstract

Since the initial discovery of surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF), these techniques have shown huge potential for applications in biomedicine, biotechnology, and optical sensors. Both methods rely on the high electromagnetic fields created at locations on the surface of plasmonic metal nanoparticles, depending on the geometry of the nanoparticles, their surface features, and the specific location of analyte molecules. Lately, ZnO-based nanostructures have been exploited especially as SERS substrates showing high enhancement factors and increased charge transfer effect. Additionally, applications focused on enhancing the fluorescence of analyte molecules as well as on tuning the photoluminescence properties of ZnO nanostructures through combination with metal nanoparticles. This review covers the major recent results of ZnO-based nanostructures used for fluorescence and Raman signal enhancement. The broad range of ZnO and ZnO–metal nanostructures synthesis methods are discussed, highlighting low-cost methods and the recyclability of ZnO-based nanosubstrates. Also, the SERS signal enhancement by ZnO-based nanostructures and the influences of lattice defects on the SERS signal are described. The photoluminescence enhancement of ZnO in the presence of noble metal nanoparticles and the molecular fluorescence enhancement in the presence of ZnO alone and in combination with metal nanoparticles are also reviewed.

Red fluorescent carbon nanoparticles derived from Spinacia oleracea L.: a versatile tool for bioimaging and biomedical applications

“…2(a) that the increase in temperature caused a gradual reduction in fluorescence intensity, which can be attributed to the presence of thermal energy inducing electronic vibrations that release non-radiative energy. 23 Furthermore, time-dependent fluorescence intensity was studied at 5 minute intervals over 30 minutes and it was found that the intensity remained constant over time, with the peak intensity consistent with that shown in Fig. 2(b).…”

Red Fluorescent Carbon Nanoparticles Derived fromSpinacia oleracea L.: A Versatile Tool for Bioimaging & Biomedical Applications

“…We can see from Figure 2(a) that the increase in temperature caused a gradual reduction in fluorescent intensity, which can be attributed to the presence of thermal energy inducing electronic vibrations that result in the release of non-radiative energy. 15 Furthermore, time-dependent fluorescence intensity was studied at 5-minute intervals over 30 minutes and found that the intensity remained constant over time, with the peak intensity consistent with that shown in Figure 2(b). Our investigation on the effects of prolonged light exposure and temperature indicates that the CNPs synthesized exhibit good photostability and thermal stability with a slight decrement in intensity as the temperature rises.…”

Fluorescence-Enhanced Microfluidic Biosensor Platform Based on Magnetic Beads with Highly Stable ZnO Nanorods for Biomarker Detection

“…One of the challenges in using fluorescence-imaging-based quantification is the low fluorescence emission of organic dyes which resulted in low sensitivity and small dynamic range, as previously described. ZnO nanostructures are well-known for their ability to amplify fluorescence at their surface, making them a promising choice as enhancers in fluorescence-based sensors . This property is due to the evanescent electric field that is generated at the surface of the nanostructure, which enhances the excitation energy of organic dyes across a broad spectrum of visible light.…”

“…ZnO nanostructures are well-known for their ability to amplify fluorescence at their surface, making them a promising choice as enhancers in fluorescence-based sensors. 44 This property is due to the evanescent electric field that is generated at the surface of the nanostructure, which enhances the excitation energy of organic dyes across a broad spectrum of visible light. FAM conjugated aptamer−cDNA duplex probes were utilized to verify the effective immobilization of the aptamer−cDNA duplex on the MBs-ZnO NRs (Figure S6).…”