Fluorescence detection of carbon quantum dots assessed by stratospheric platform

Measurement of molecular fluorescence is one of the most sensitive methods to detect the signal of interest. It can be realized in numerous arrangements including flow-through geometry (i. e. chromatography, capillary electrophoresis) [1,2], imaging and microscopy [3,4], however the most commonly used is the stationary fluorescence spectrometry [5]. The diversity of the detectors is based on several factors such as light source and/or geometry of the detection cell. Currently, the utilization of the light emitting diodes as a light source is a trend enabling miniaturization of the instrumentation [6-8]. The portable devices moreover allow the in situ analyses, which have number of advantages such as obtaining the data in real time, lowering the time of the analysis as well as its costs. Especially in cases where the detection site is difficult to reach, the remote-controlled analyzers are beneficial. Stratosphere is one of these hard-to reach places and therefore stratospheric or space research is a new challenge for these devices [9]. Nowadays, balloons are a main tool for stratospheric in situ research mostly focused on the stratosphere composition. In case that balloon is above the ozone layer, nearly the same radiation as in free space affects the balloon. This fact is used to test durability of space materials in cheap way [10]. Ghysels et al. used optical sensor carried by balloon to quantify amount of carbonic dioxide in upper parts of troposphere and stratosphere [11]. Photometric quantification was also used to quantify vertical distribution of oxides of bromine [12]. However, to our knowledge, no fluorimetric device has been used in stratospheric conditions so far. To monitor the behavior of the detector above the ground, carbon quantum dots (CQDs) can be employed. CQDs are new type of nanomaterial. They retain portion of bulk material properties and gain new, which arise from their nanometer diameter. They are biocompatible and possess chemical inertness and low toxicity [13]. The importance of CQDs is reflected in their electronic, mechanical, chemical and optical properties. All of these properties allow using CQDs in different fields of research such as catalysis, sensing, bioimaging, tissue engineering, optoelectronic and electronic devices [14-16]. The fluorescent labeling of DNA using nanoparticles enables DNA to be observable in in vivo or in vitro experiments [17]. The aim of this work was to test the fluorescence analyzer made by 3D printer in stratospheric conditions. For testing of this stratospheric equipment 0-32 mg.ml-1 CQDs were used. Testing was performed prior and after the return of stratospheric probe from the stratosphere

Figure 1: (A) 3D printer with detection part of probe. (B) 3D model of stratospheric probe detection part.

Figure 2: (A) 3D model of flight computer Julo-X and its real photo (Aa). B) Schematic illustration of miniaturized fluorescence analyzer connected with Julo-X.

Figure 3: (A) Test of communication between the stratospheric probe and the control center. (B) Filling of latex balloon with helium. (C) Localization of the stratospheric probe by radio signal.

Figure 4: (A) Fluorescent activity of 0-32 mg.ml-1 CQDs determined by stratospheric probe a) before launch, b) after landing probe. (B) Fluorescent activity of 0-32 mg.ml-1 CQDs determined by fluorescence analyzer a) before launch in the laboratory, b) after landing probe in the laboratory.

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