It is commonly accepted that several processes are involved, including an enhanced excitation field, an increased radiative decay rate of the emitter, as well as an increased coupling efficiency of the fluorescence emission to the far field through the nanoparticle scattering
It is commonly accepted that several processes are involved, including an enhanced excitation field, an increased radiative decay rate of the emitter, as well as an increased coupling efficiency of the fluorescence emission to the far field through the nanoparticle scattering. find common applications in immunoassays as well as other fluorescence-based assays. Azlocillin sodium salt Intro Fluorescence spectroscopy is definitely a powerful tool in medical and biological analysis.1 Employing fluorescence to detect the biomarkers, or fluorescence immunoassay is just about the technology of choice for the medical and clinical diagnostics.2 For the early analysis of some diseases, a low concentration of biomarkers needs to be detected and quantified, so there is a continuing demand to improve the limit of detection (LOD) of a fluorescence immunoassay. Such improvement is generally closely related to an enhanced fluorescence signal intensity. The surface enhanced fluorescence (SEF) effect attracts Serpinf1 a lot of attention and has been explored extensively to meet this need.3C5 The SEF effect, also known as the MEF (metal-enhanced fluorescence) effect, refers to the intensity enhancement of the fluorescence signals from the emitters in the proximity of metallic nanoparticles or nanostructures.6C8 Besides the intensity enhancement, some other appreciable effects have also been observed, such as the decreased lifetime and the increased photostability.9 Ever since the earliest theoretical studies in the 1980s,10,11 much progress has been made in the understanding of the SEF effect. It is commonly accepted that several processes are involved, including an enhanced excitation field, an Azlocillin sodium salt increased radiative decay rate of the emitter, as well as an increased coupling efficiency of the fluorescence emission to the far field through the nanoparticle scattering. The radiating plasmon model (RPM) has been raised by Lakowicz to address this latter issue,12 and experimental evidences have also been observed recently.13 Along with the better understanding in Azlocillin sodium salt the mechanism, a lot of effort has also been made to push the SEF effect to real applications, including the SEF-based immunoassays.14,15 To date, various SEF-based immunoassay schemes have been successfully demonstrated, most of which consist of two separate components: the SEF substrate, and the immunoassay component same as that in the conventional fluorescence immunoassay scheme.16C20 The SEF substrate has become the focus of the design. Different metallic nanostructures, such as silver island films,16 self-assembled metallic nanoparticles17,18 and metallic arrays19 have been used as the SEF substrates. Despite the remarkable fluorescence enhancements obtained using these schemes, only a very few have exhibited a significantly improved LOD.17,19 The insufficient analytical performance in most such assay schemes is attributed to the inhomogeneity of the SEF substrates.17 A kind of gold plasmonic substrate was recently developed by Dai for SEF in the near-infrared region.21C24 With improved homogeneity of the substrate, not only was the fluorescence greatly enhanced, but the LOD was also significantly improved. However, some other problems still exist. In the above assay architecture, a fluorescent labeled antibody is usually always used to detect the target antigen. Relatively complex chemistries are involved in the process of molecular labeling, which limits the application range and may also increase the overall cost of the immunoassay. In addition, the effect of labeling around the functionality of the antibody should also be evaluated.25 A different architecture of SEF-based immunoassay was raised by our group to address the above-mentioned issue. Instead of the conventionally used dye-labeled antibodies, the scheme used a fluorescent immune substrate and antibody functionalized silver nanoparticles to obtain the doseCresponsive fluorescence signals, and was hence applicable to a wide range of antibodies. 26 The analytical performance was experimentally exhibited. However, the LOD was moderate due to the strong inherent fluorescence of the substrate, which leads to a high blank signal. A higher blank signal generally leads to an increased standard deviation between multiple impartial measurements, resulting in a higher LOD. Recently, metallic (Au or Ag) films has been introduced to replace.
