Recently, Dr. Yan Liu, BAQIS Assistant Researcher from Atomic Ensemble Precision Measurement Group, in collaboration with scientists from Germany, France and Russia, reported their latest progress towards bio-imaging and temperature-sensing in the living cell in Nano Letters with the title "Silicon-Vacancy Nanodiamonds as High Performance Near-Infrared Emitters for Live-Cell Dual-Color Imaging and Thermometry".

Besides the very-known applications of jewelry decoration, industrial cutting and so on, diamond also acts an important role in quantum technology for its optically active color centers. The silicon vacancy (SiV) color center, owing to its D3d symmetry, its electronic energy levels receive relatively low phonon effects, and 70% of its fluorescence emission concentrates on its zero-phonon-line at 738 nm which typically has a linewidth of 5 nm at room temperature as shown in Fig.1. Other color centers, such as NV center, which receive strong phonon effects, shows a wide fluorescent spectrum exceeding 100 nm.

Fig. 1 The scheme of SiV nano diamonds as fluorescent marker in the living cell and sensing with its zero-phonon line.

In the bio-sensing research field, for its low-toxicity and stable fluorescence, nano-diamonds containing SiV center was used as fluorescent labelling in the living cell for studies of bio-chemical processes, drug mechanism and so on. The SiV center has a narrow fluorescent emission band, and is suitable for optical filtering from the optical backgrounds in the living cell, as it is illustrated in Fig. 1. The concentrated 738 nm fluorescence, is in near-infrared band, has a good transmittance through cells and tissues and could be applied for optical imaging of deeper living cells or tissues.

Fig.2 The process of producing SiV nano-diamonds for fluorescent labelling in the living cell.

Fig.3 (a) Fluorescent labelling in the living cell by SiV nano-diamonds; (b) the spectral shifts of a SiV color center at different temperatures; (c) upper image, the trajectory path of a SiV nano-diamond in the living cell, lower image, tracking of the fluorescent intensities showing good fluorescent stability.

The paper reported the generation of SiV nano-diamonds by high temperature high pressure method, and the purification process as well as chemical coating, as shown in Fig. 2. Then the SiV nano-diamonds were put into the cell culture well where SiV nano-diamonds were absorbed by living cells on a home-built confocal microscope by Yan Liu. The trajectory path of the single SiV nano-diamonds were also tracked and the zero-photon-line shifts were measured. The study shows that the shift of SiV zero-phonon line can be used for temperature sensing, as well as the linewidth of the zero-phonon line, as shown in Fig.3.

In this work, Dr. Yan Liu built the fluorescent confocal microscope and performed the experiments of living cell imaging, single SiV nano-diamond tracking and the zero-phonon line spectral measurements. “The study can also be extended to various drug mechanism studies and tests of different in-cell curing therapies, micro-diamonds may perform a better role than colloidal gold in vitro for Disease diagnosis, achieving faster PCR test with higher sensitivity, and be beneficial to disease diagnosis at very early stage…” commented by Yan Liu.

Reference:

Weina Liu, Md Noor A. Alam, Yan Liu, Viatcheslav N. Agafonov, Haoyuan Qi,Kaloian Koynov, Valery A. Davydov, Rustem Uzbekov, Ute Kaiser, Theo Lasser, Fedor Jelezko*, Anna Ermakova*, and Tanja Weil* 2022. "Silicon-Vacancy Nanodiamonds as High Performance Near-Infrared Emitters for Live-Cell Dual-Color Imaging and Thermometry." Nano Lett. 2022, 22, 7, 2881–2888