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0Spherical microlasers with carbon dots and organic dyes
A.A. Starovoytov1, E.O. Soloveva1, K. Kurassova1, K.V. Bogdanov1, I.A. Arefina1, N.N. Shevchenko2, A.A. Mitusova3, T.A. Vartanyan1, D.R. Dadadzhanov1, N.A. Toropov14*
1-International Research and Education Center for Physics of Nanostructures, ITMO University, 49 Kronverksky Pr., St. Petersburg 197101, Russia 2- Institute of Macromolecular Compounds, Russian Academy of Sciences, Bolshoy pr. 31 St. Petersburg
199004, Russia
3- Pavlov First Saint Petersburg State Medical University, L'va Tolstogo str. 6-8, St. Petersburg 197022, Russia 4- Optoelectronics Research Centre, University of Southampton, Southampton SO17 1BJ, UK
* nikita.a.toropov@gmail.com
Microlasers based on whispering gallery modes (W GMs) have attracted attention in recent years as biosensors due to their biocompatibility, compact size, high Q-factor and narrow spectral width of resonance lines [1,2]. These properties make sensors based on such microlasers extremely sensitive to the slightest changes in the refractive index of the environment [3]. Popular fluorescent dopants for the development of WGM emitting cavities are quantum dots, but their application may be limited due to potential toxicity caused by the presence of heavy metals in their composition. The counterparts of quantum dots - carbon dots (CDs) - are much more biocompatible and non-toxic, which makes them safe for use in biological systems [4].
In this work, we propose a low-cost methodology to fabricate carbon-dot-doped WGM-based spherical microresonators (preliminary tested with rhodamine molecules) to develop a biocompatible sensor that is suitable for in vivo cell tagging and tracking applications. The sensing properties were tested by depositing bovine serum albumin (BSA), a protein commonly used as a reference protein to study interactions with drugs and nanoparticles, onto CDs-doped spheres. The effect of polystyrene microresonators on THP-1 and B16 cell lines survival was also investigated.
For the sensing experiments, 4 ^L of aqueous bovine serum albumin solution was added to the tested sample of PS microresonators and left to dry out under room conditions. A concentration series of experiments was performed with 10-12, 10-15, 10-16, 10-18 M BSA to determine the limit of detection. The mode shift in the emission spectra is caused by the change in the refractive index of the surrounding medium, so-called reactive sensing. A sufficiently large frequency shift is observed even at a concentration of 10-15 M; it is about 1.5 nm and becomes smaller with decreasing BSA concentration. A reproducible character of frequency shifts was demonstrated on the normalized emission spectra, however, at 10-18 M it becomes spectrally unresolvable for the used sensor. Thus, the detection limit was 10-16 M and the dynamic range was at least four orders of concentration.
In order to study the biocompatibility of PS microresonators, experiments were performed to introduce CDs-doped microspheres into THP-1 cells. The transmitted light image obtained by laser scanning confocal microscope shows that added polystyrene spheres doped with CDs accumulate on the cell damage. In addition, cell survival tests were performed when CDs and PS microspheres doped with CDs were added to cells. THP-1 and B16 cell lines were selected for the survival tests. The obtained dependence of the percentage of cell survival on the concentration of the additive shows that in most cases the percentage of survival is higher when the CDs are embedded in PS microspheres.
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