Carbon Nanodot–Neutral Red-Based Photometric and Fluorescence Sensing for Trace Detection of Nitrite in Water and Soil Using Smartphone

Abstract

Nitrite level estimation in soil and water bodies is critical to monitor the ecosystem of our environment and agricultural yield. Herein, we report a carbon nanodots (C-dots) and neutral red (NR)-based photometric and fluorescence mode sensing scheme using which trace detection of nitrite in water and soil has been done. The proposed scheme utilizes a handheld compact sensing platform developed on a smartphone. For the present sensing studies, the C-dots and NR act as donors and acceptors, respectively, in the frequency resonance energy transfer (FRET) process. The presence of nitrite in the C-dot–NR mixture affects the FRET process, which causes a decrease in the absorption wavelength conditions at 560 nm while increasing the fluorescence intensity at 563 nm upon excitation with a source of wavelength 375 nm. These variations have been correlated to quantify the concentration of the nitrite level in the medium. With the designed sensing system, variations of nitrite concentration from 0.1 to 3.0 μg/mL have been measured with a high degree of accuracy. The designed sensor has been implemented to estimate the nitrite level of infield water and soil samples, and the experimental results are compared with the laboratory standard tools. With the advantages of being low-cost, field portable, and relatively convenient to handle, it is anticipated that the proposed smartphone sensor could emerge as a potential avenue for onsite assessment of other parameters of water and soil as well.

Sensor design strategy for environmental and biological monitoring

“…There are also a few reports on the use of carbon nanodots as fluorescence probes for the real-time monitoring of soil conditions. 58,59 Detecting air pollutants, including small organic pollutants and ammonia gas, is important because it can have immediate effects on the human respiratory system. 60 In particular, many researchers have agreed that it is very important to achieve the quantitative and reproducible on-site detection of these air pollutants.…”

“…It should be noted that this sensor made it possible to achieve real‐time monitoring of the picric acid flow rate (1.6 mL/min, and picric acid of 400 μM) and accumulation rate (0.0064 μmol/min) in the roots. There are also a few reports on the use of carbon nanodots as fluorescence probes for the real‐time monitoring of soil conditions 58,59 …”

An insight into the role of carbon dots in the agriculture system: a review

“…This facilitates convenient on-site assessment of nitrite in soil. 269 Such CDs and smartphone-based agriculture sensors have potential for the onsite assessment of other parameters (micro- and macro-nutrients, temperature, moisture, etc. ) of soil.…”

A novel fluorescent indicator‐based fluorene derivative for rapid and visual trace water sensing

“…Fluorescent methods have emerged as promising options due to their cost-effectiveness, low detection limits, and suitability for in situ assay [1,6]. Several fluorescent detection systems have been developed for water assay by combining traditional sensing mechanisms, including intramolecular charge transfer (ICT) [7], photo-induced electron transfer (PET) [8], excimer and exciplex [9], aggregation-induced emission (AIE) [10], excited-state intramolecular proton transfer (ESIPT) [11], hydrolysis reactions of Schiff bases [12] and ferrocene derivatives [13], and hydration of aldehydes [14], with various materials such as small molecular organic fluorescent probes [15], metalorganic frameworks (MOFs) [16], carbon dots (CDs) [17], polymers [18,19], and copper nanoclusters [20]. Despite the considerable achievements observed in this domain owing to their exceptional sensitivity and accuracy, the majority of existing fluorescent techniques are plagued by issues such as diminished fluorescence signal output [20][21][22][23][24][25], limited portability, demanding processing protocols, and susceptibility to interference from environmental factors like pH [26] and polarity [27,28].…”