Thermometric Characterization of Fluorescent Nanodiamonds Suitable for Biomedical Applications

Abstract

Nanodiamonds have been studied for several biomedical applications due to their inherent biocompatibility and low cytotoxicity. Recent investigations have shown perspectives in using fluorescent nanodiamonds as nanothermometers because of their optical properties’ dependence on temperature. Easy and accurate localized temperature sensing is essential in a wide variety of scientific fields. Our work demonstrated how the fluorescence spectrum of high-pressure high-temperature fluorescent nanodiamonds of three different sizes: 35 nm, 70 nm and 100 nm, changes with temperature within an important biological temperature range (25 °C to 60 °C). Taking advantage of this phenomenon, we obtained nanothermic scales (NS) from the zero phonon lines (ZPL) of the NV0 and NV− colour centres. In particular, the 100 nm-sized features the more intense fluorescence spectra whose linear dependence with temperature achieved 0.98 R2 data representation values for both NV0 and NV−. This model predicts temperature for all used nanodiamonds with sensitivities ranging from 5.73% °C−1 to 6.994% °C−1 (NV0) and from 4.14% °C−1 to 6.475% °C−1 (NV−). Furthermore, the non-cytotoxic interaction with HeLa cells tested in our study enables the potential use of fluorescence nanodiamonds to measure temperatures in similar nano and microcellular aqueous environments with a simple spectroscopic setup.

Nano- and micro-crystalline diamond film structuring with electron beam lithography mask

“…It is worth noting that all the samples exhibit a strong photoluminescent (PL) signal centred at approximately 575 nm zero phonon line, corresponding to defects involving nitrogen vacancies in their neutral state. The recorded values are consistent with previous research findings [20][21][22]. Variations in the positions of these peaks can be attributed to factors such as temperature fluctuations and internal mechanical stress arising from differences in thermal expansion coefficients between the diamond, substrate, and the inclusion of graphitic phases [23][24][25].…”

Fluorescent Nanodiamonds for Nanoscale Thermometry in Biology

“…Their spectra have zero-phonon lines (ZPL) at 575 and 637 nm, respectively, with broad phonon sidebands at room temperature [16]. Both NV charge states can be used for temperature sensing by observing the redshift of ZPL with a temperature increase [17][18][19][20]. Such a method is attractive due to the experimental simplicity since all operations and detection can be done purely optically.…”

“…Such a method is attractive due to the experimental simplicity since all operations and detection can be done purely optically. Many works focus on intracellular thermometry by detecting ZPL shift [17][18][19][20]. As one example, the work of the group from Jinan University can be chosen (Figure 2a) [20].…”

Femtosecond Optical Nonlinearity of Nanodiamond Suspensions

“…These works are aimed at investigating, e.g., optical limiting (a nonlinear decrease of the transmitted light intensity) [1] and saturable absorption (a nonlinear increase of the transmitted light intensity) [2] to develop and create optical limiters of nanosecond laser pulses [3][4][5][6][7][8][9][10][11][12][13] and passive laser shutters for generating picosecond and femtosecond laser pulses [14][15][16][17][18][19][20][21][22][23][24], respectively. Nanodiamond, being another form of nanocarbon material, is also attractive due to its unique properties [25][26][27][28][29][30][31][32][33]. Among the various methods for producing nanodiamonds [27,34], the most prevalent are the detonation synthesis method [35] and the method of grinding diamonds synthesized at high pressure and high temperature (HP-HT) [36].…”