Highly Sensitive Detection and Rapid Removal of Picric Acid Using Fe2O3-CdSe Nanocomposite As Fluorescent Probe
Authors: Kumar Anshu , Nath Prathul , Kumar Vishal , Satapathi Soumitra 
Published: July 2021

Detection of the nitro-fragrant compound at trace level is critical in combating terrorism, for keeping up homeland security, accompanying environmental and clinical safety. Among various nitroaromatics compounds (NACs), the importance of picric acid (PA), also known as 2,4,6-Trinitrophenol (TNP), due to its extensive usage in the production of deadly explosives, fireworks, rocket fuels, leather processing and sensitizers in photographic emulsions. Moreover, it is an odorless, colorless pale yellow solid which profoundly contaminant to soil due to high solvency in an aqueous medium, ends up in adverse effects. The ecological contamination caused by this results in respiratory problems, intense irritation to the skin and eyes, high doses may cause prospective harms in organs and causes cancer, sensitization, destruction, kidney damage, acute hepatitis and diarrhea, etc.[1] The metabolism of these explosive nitro-aromatic compounds end up in generation of reactive nitrogen oxide species, that promptly react with biological macromolecules and cause formation of potent genotoxic and mutagenic metabolites.[2] Therefore, detection and quantitative estimation of those hazardous chemicals are highly indispensable.
In the past, there are a number of reports on multifunctional sensors for the detection of NACs, given the appreciable sensitivity and selectivity. As of now, many fluorescence chemosensors/probes have been effectively applied for the detection of PA with functional specificity based on its characteristic properties, particularly resonance energy transfer and electron-deficient nature of the nitro group (-NO2), yet only a few appeared closer to the practical applications.[3] Recent reports on nanoparticle and quantum dot (QD) probes exhibited remarkable chemosensory response towards NACs compared with the conventional organic small molecules, polymers and metal-organic frameworks (MOFs) because of their unique optical properties and thanks to the confinement of electronic states of quantum dots.[4] Recently, thiols capped semiconductor NPs, synthesize through water treatment, has given a fascinating and alternate methodology to synthesize semiconductor NPs. Among these, CdSe nanoparticles are the extensively examined semiconductor NPs primarily attributable to their well-tuned emissive properties process and moderately mature synthetic methods. Late reports on CdSe nanoparticles and expedient to surface modification showed its fate in the detection of NACs.[3] Quantum dots have a clear advantage over molecule-based emitters; however, these multi-model sensors are inexpedient for the evacuation of the earmark species, which might be a source of secondary contamination. From this perspective, the fuse of a fluorescent and magnetic functionality in a solitary nanocomposite molecule would be a promising alternative. This study aimed to focus on the development of this kind nanocomposite, serving a challenge that magnetic NPs possess a strong photoluminescence quenching in the merely fluorescent moiety. Various reports reveal that this undesirable photoluminescence quenching in heterodimer structures comprised of immediate contact between the semiconductor and magnetic domain can be caused by strong electronic coupling.[5] Reasoning from this fact, extra care must be taken to suppress undesirable preventive interactions within the nanocomposite that would revoke the unwelcome properties.
In this work, we reported a hybrid nanostructure, comprises a magnetic core of Fe2O3 NPs encapsulated inside a thin silica shell, electrostatically adsorbed with a positively charged spacer arm of florescent Cysteamine-capped CdSe quantum dots (QDs). This promising novel hybrid nanostructure, namely magneto-fluorescent nanosensor (particle size ≈ 12.7 nm), stabilized through strong electrostatic attraction between 3-((Triethoxylsilyl)propylcarbamoyl) butyric acid-anchored Fe2O3@SiO2 NPs and Cysteamine-capped CdSe QDs, electrostatically attached to the free anionic carboxyl group in the spacer arm of Fe2O3@SiO2 NPs. This multimodal nanosensor probe showed a strong specific response to Picric Acid over a number of other explosive (NACs) in DMSO, making them promising fluorescence probes for PA detection and removal, simultaneously, for real-time application. The quenching constant (KPA) of nanosensor with PA was obtained to be 4.3×104 M-1 in DMSO with a limit of detection (LOD) up to 2.2 µM as a consequence of turn off sensing.[6] The sensing mechanism is probed via UV–Vis spectroscopy, steady-state and time-resolved fluorescence spectroscopy. In addition to solution-phase sensing, this nanosensor also showed an excellent ability for the removal of detected PA molecules with the use of an external magnet, staging as a possibility for the potential application of low-cost and stand-off sensor.

References:

[1] V. Kumar, N. Choudhury, A. Kumar, P. De, S. Satapathi, Poly-tryptophan/carbazole based FRET-system for sensitive detection of nitroaromatic explosives, Optical Materials 100, 109710 (2020); doi: 10.1016/j.optmat.2020.109710
[2] V. Kumar, B. Maiti, M.K. Chini, P. De, S. Satapathi, Multimodal Fluorescent polymer sensor for Highly sensitive Detection of Nitroaromatics, Scientific Reports 9(1), 7269 (2019); doi: 10.1038/s41598-019-43836-w
[3] V. Kumar, A. Kumar, P. Nath, S. Satapathi, Fabrication of Cysteamine capped-CdSe QDs anchored graphene xerogel nanosensor for facile onsite visual detection of TNT, Nano-Structures & Nano-Objects 25, 100643 (2020); doi: 10.1016/j.nanoso.2020.100643
[4] F. Akhgari, H. Fattahi, Y.M. Oskoei, Recent advances in nanomaterial-based sensors for detection of trace nitroaromatic explosives, Sensors and Actuators B: Chemical 221, 867-78 (2015); doi: 10.1016/j.snb.2015.06.146
[5] S. Satapathi, V. Kumar, M.K. Chini, R. Bera, K.K. Halder, A. Patra, Highly sensitive detection and removal of mercury ion using a multimodal nanosensor, Nano-Structures & Nano-Objects 16, 120-126 (2018); doi: 10.1016/j.nanoso.2018.05.006
[6] V. Kumar, A. Kumar, M.K. Chini, S. Satapathi, Fluorescent Fe2O3-CdSe nanocomposite probe for selective detection and removal of picric acid, Materials Chemistry and Physics 260, 124130 (2020); doi: 10.1016/j.matchemphys.2020.124130

Figure 1