Light creation without pump: tuning plasmonic resonance for surface enhanced chemiluminescence

Chemiphores are entities, which exhibit wide-band light emission without any external light source but just due to the chemical reaction resulting in the chemiluminescence effect. Since the chemiphores usually have low quantum... [ view full abstract ]

Chemiphores are entities, which exhibit wide-band light emission without any external light source but just due to the chemical reaction resulting in the chemiluminescence effect. Since the chemiphores usually have low quantum efficiency, chemiluminescence is a weak optical effect. Surface plasmon resonance in metallic nanoparticles (NP), however, can enhance the chemiluminescence of molecules due to the acceleration of radiative transitions. To enhance the chemiphores-particles interaction, metal NP has to be placed at the optimum distance from the chemiphors. The shape and material of the particles has to be accurately chosen to ensure the overlapping of their plasmonic band with the emission band of the chemiphores.

The proof of concept experiment was carried out in a microfluidic chip. Although the commercially available NP with non-optimized position of the plasmon resonance were employed, considerable enhancement of the chemiluminescence intensity was obtained [1]. To test the opportunities for further chemiluminescence enhancement we studied the optical properties of silver NP of different shape and size. 

According to our calculations, optimum overlapping with the luminol emission bands at 452 and 489 nm is achieved for hemispherical NP with diameter of 18 and 73 nm on a quartz substrate as shown in Figure 1. The feasibility of obtaining of such NP arrays is confirmed by the extinction spectra of the ensembles of NP on quartz substrates fabricated via physical vapor deposition. Figure 2 plots the corresponding extinction spectra of granular silver films with equivalent thicknesses of 3 and 9 nm [2]. Contrary to that optical properties of NP obtained via laser ablation in liquids is less tunable. The red wing of the plasmon band peaked at 400 nm overlaps with the luminol luminescence bands. In addition, the arrangement of particles on the surface of transparent dielectric material makes it possible to control the distance between NP and chemiphores and opens up the possibility of integrating the substrates modified with the NP into the flowing microfluidic systems. 

[1] A. Karabchevsky et al., 'Tuning the chemiluminescence of a luminol flow using plasmonic nanoparticles', Light Sci Appl. 5, e16164 (2016). 

[2]Leonov et al. Opt. Spectrosc. (2015) 119: 450. https://doi.org/10.1134/S0030400X15090179