Singlet Oxygen Detection on a Nanostructured Porous Silicon Thin Film via Photonic Luminescence Enhancements

Because reactive oxygen species are involved in a range of pathologies, developing analytical tools for this group of molecules opens new vistas for biomedical diagnostics. Herein, we fabricate a porous silicon microcavity (pSiMC) functionalized with luminescent singlet oxygen (¹O₂) probe <i>EuA</i> ((Eu­(III)-2,2′,2″-(10-(2-((4-(2-((4-(2-((anthracen-9-ylmethyl)­amino)­ethyl)-1<i>H</i>-1,2,3-triazol-1-yl)­amino)-2-oxoethyl)-2-oxo-1,2-dihydroquinolin-7-yl)­amino)-2-oxoethyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)­triacetic acid) as proof of concept of an optical sensor for reactive oxygen species. We characterize each surface modification step of the pSiMC by means of FTIR and X-ray photoelectron spectroscopy as well as by determining the optical shifts of the resonance wavelength of the pSiMC. The luminescence signal upon detection of ¹O₂ on the <i>EuA</i>-modified pSiMC is enhanced ∼2-fold compared to that of a single layer and a detuned microcavity. The sensing performance of the <i>EuA</i> probe is improved significantly on the pSiMC compared to that in aqueous solution, giving a limit of ¹O₂ detection of 3.7 × 10^–8 M

Rapid Fluorescence Quenching Detection of <i>Escherichia coli</i> Using Natural Silica-Based Nanoparticles

The development of fluorescent silica nanoparticles (SNP-RB) from natural amorphous silica and its performance as an Escherichia coli (E. coli) biosensor is described in this paper. SNP-RB was derived from silica recovered from geothermal installation precipitation and modified with the dye, Rhodamine B. The Fourier Infrared (FTIR) confirms the incorporation of Rhodamine B in the silica matrix. Transmission Electron Microscopy (TEM) micrographs show that the SNP-RB had an irregular structure with a particle diameter of about 20–30 nm. The maximum fluorescence spectrum of SNP-RB was recorded at 580 nm, which was further applied to observe the detection performance of the fluorescent nanoparticles towards E. coli. The sensing principle was based on the fluorescence-quenching mechanism of SNP-RB and this provided a wide linear E. coli concentration range of 10–105 CFU/mL with a limit detection of 8 CFU/mL. A rapid response time was observed after only 15 min of incubation of SNP-RB with E. coli. The selectivity of the biosensor was demonstrated and showed that the SNP-RB only gave quenching response only to live E. coli bacteria. The use of SNP-RB as a sensing platform reduced the response time significantly compared to conventional 3-day bacterial assays, as well having excellent analytical performance in terms of sensitivity and selectivity

Rapid Fluorescence Quenching Detection of Escherichia coli Using Natural Silica-Based Nanoparticles

The development of fluorescent silica nanoparticles (SNP-RB) from natural amorphous silica and its performance as an Escherichia coli (E. coli) biosensor is described in this paper. SNP-RB was derived from silica recovered from geothermal installation precipitation and modified with the dye, Rhodamine B. The Fourier Infrared (FTIR) confirms the incorporation of Rhodamine B in the silica matrix. Transmission Electron Microscopy (TEM) micrographs show that the SNP-RB had an irregular structure with a particle diameter of about 20&ndash;30 nm. The maximum fluorescence spectrum of SNP-RB was recorded at 580 nm, which was further applied to observe the detection performance of the fluorescent nanoparticles towards E. coli. The sensing principle was based on the fluorescence-quenching mechanism of SNP-RB and this provided a wide linear E. coli concentration range of 10&ndash;105 CFU/mL with a limit detection of 8 CFU/mL. A rapid response time was observed after only 15 min of incubation of SNP-RB with E. coli. The selectivity of the biosensor was demonstrated and showed that the SNP-RB only gave quenching response only to live E. coli bacteria. The use of SNP-RB as a sensing platform reduced the response time significantly compared to conventional 3-day bacterial assays, as well having excellent analytical performance in terms of sensitivity and selectivity

Lanthanide Luminescence Enhancements in Porous Silicon Resonant Microcavities

In this paper, the covalent immobilization and luminescence enhancement of a europium (Eu­(III)) complex in a porous silicon (pSi) layer with a microcavity (pSiMC) structure are demonstrated. The alkyne-pendant arm of the Eu­(III) complex was covalently immobilized on the azide-modified surface via ligand-assisted “click” chemistry. The design parameters of the microcavity were optimized to obtain an efficient luminescence-enhancing device. Luminescence enhancements by a factor of 9.5 and 3.0 were observed for Eu­(III) complex bound inside the pSiMC as compared to a single layer and Bragg reflector of identical thickness, respectively, confirming the increased interaction between the immobilized molecules and the electric field in the spacer of the microcavity. When comparing pSiMCs with different resonance wavelength position, luminescence was enhanced when the resonance wavelength overlapped with the maximum emission wavelength of the Eu­(III) complex at 614 nm, allowing for effective coupling between the confined light and the emitting molecules. The pSiMC also improved the spectral color purity of the Eu­(III) complex luminescence. The ability of a pSiMC to act as an efficient Eu­(III) luminescence enhancer, combined with the resulting sharp linelike emission, can be exploited for the development of ultrasensitive optical biosensors