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. 2019 Jun 20;4(6):10702-10713.
doi: 10.1021/acsomega.9b00858. eCollection 2019 Jun 30.

Nitrogen-Doped Graphene Oxide Dots-Based "Turn-OFF" H2O2, Au(III), and "Turn-OFF-ON" Hg(II) Sensors as Logic Gates and Molecular Keypad Locks

Naveen Kumar Reddy Bogireddy  1 , Victor Barba  2 , Vivechana Agarwal  1
Affiliations

Nitrogen-Doped Graphene Oxide Dots-Based "Turn-OFF" H2O2, Au(III), and "Turn-OFF-ON" Hg(II) Sensors as Logic Gates and Molecular Keypad Locks

Naveen Kumar Reddy Bogireddy et al. ACS Omega. .

Abstract

Fluorescent nitrogen-doped graphene oxide dots (NGODs) have been demonstrated as an on-off nanosensor for the detection of Hg2+, Au3+, and H2O2. As compared to l-cystine, where the luminescence signal recovery results from the detachment of Hg2+ from the NGODs, signal recovery through l-ascorbic acid (turn-off-on model) has been attributed to the reduction of Hg2+ to Hg0. The sustainable recovery of the photoluminescence signal is demonstrated using common citrus fruits containing vitamin C (l-AA), suggesting a promising practical usage of this sensing system. Additionally, the sensitivity of NGOD- and AA-originated signal recovery from the Hg(II)-NGODs mixture has been successfully tested in Hg2+ ion-spiked tap water from three different places. Mimic devices were executed and verified on the basis of characteristic spectral changes, and the possible utility of this system in electronic security and memory element devices has also been demonstrated. Considering an easy synthesis process and excellent performance of NGODs, this investigation opens up new opportunities for preparing high-quality fluorescent NGODs to meet the requirements of many applications.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
(a) TEM image of as-prepared NGODs and (b) size distribution analysis from (a). (c) Fluorescence emission spectra of NGODs after excitation of 290–400 nm, (d) analysis of excitation wavelength vs intensity from PL spectra, and (e) UV–visible spectra and PLE spectra of NGODs at 441 nm. The inset shows NGODs illuminated under daylight and UV light 365 nm.
Figure 2
Figure 2
(a) XRD patterns of as-prepared NGODs (the inset shows enlarged view of the NGOD peak); deconvoluted XPS spectra of (b) C 1s, (c) O 1s, and (d) N 1s peaks of NGODs.
Figure 3
Figure 3
PL quenching pattern of NGODs in deionized water with the presence of different concentrations of H2O2 (a) PL vs wavelength for λex = 344 nm, (b) PL peak intensity vs H2O2 concentration (the inset shows linear fit at low concentrations; R2 = 0.974), and (c) possible quenching mechanism due to H2O2 adsorption on NGODs, wherein the alcohol groups are oxidized to aldehyde groups.
Figure 4
Figure 4
Selectivity of Hg2+ and Au3+ using NGODs as probes using PL spectroscopy (a) PL intensity vs wavelength at λex = 344 nm for different metal ions at 250 μM concentration (except Au3+ at 300 μM) and (b) corresponding normalized graph at λem = 441 nm (F0 = NGOD PL intensity in deionized water and F1 = PL intensity with the metal ions). The selectivity was additionally checked with Ag+, Mn2+, Mg2+, and Zn2+ (ref to Figure S3).
Figure 5
Figure 5
(a,c) PL quenching pattern of the signal intensity of NGODs in deionized water after the presence of Hg2+ and Au3+ ions, and their corresponding (b,d) concentration vs intensity analysis graphs (the inset shows linear fit of respective analysis graphs; R2 values corresponding to Hg2+ and Au3+ are 0.954 and 0.995, respectively) and high-resolution TEM images of before (e) and after the addition of (f) agglomeration due to the formation of the Hg2+–NGODs complex.
Figure 6
Figure 6
(a) Comparison of PL recovery: PL intensity ratio before and after the addition of 100 μM of l-AA, l-Cys, l-Glu, and l-Tyr (F1 and F2 correspond to PL intensities before and after the addition of the PL recovering agents, respectively) and (b) % regained PL at three different concentrations of AA and cystine.
Scheme 1
Scheme 1. Schematic Illustration of the Proposed Mechanism: Hg2+ Detection and PL Recovery Using AA and Cystine (Upper Part of the Schematic) and Au3+ Detection Using l-Cys (Bottom Part of the Schematic)
Figure 7
Figure 7
Comparison of sustainable PL recovery from Hg2+ detection: PL intensity ratio before and after the addition of different concentrations of various citrus fruits: (a) green lemon, (b) fanta lemon, (c) mandarin orange, (d) tangerine orange, and (e) cotton candy grapes. The citrus fruit juice was filtered using a filter paper and then diluted to 1/100 times with respect to the original concentration.
Figure 8
Figure 8
(a) Schematic representation of logic functions of NGODs with two chemical inputs Hg2+ and l-Cys/l-AA and (b) truth table for input A and output A (Al) with its corresponding digital input and output signals representing NOT gate, and (c) truth table for input 1 (from the output of input A) and input 2 (l-Cys/l-AA) strings with its corresponding digital input and output signals representing OR gate, respectively. As conventionally accepted notations, the 0/OFF state represents no luminescence and 1 represents luminescence. (d) Bar diagram representing the change in the emission intensity of NGODs (chemical inputs were represented as A = l-AA; H = Hg2+; F = off state and O = on state, respectively) and (e) schematic representation of a KSL model using NGODs as the molecular fluorescence system.
Figure 9
Figure 9
Reversibility of NGOD probe with the alternate addition of (a) Hg2+ and l-Cys, (b) Hg2+ and l-AA, (c) l-Cys and Hg2+, (d) l-AA and Hg2+ (the concentration of Hg2+, l-Cys, and l-AA was maintained at 250 μM), and (e) feedback loops with write–read–erase–read function, (f) sequential logic circuit of the memory unit, and (g) truth table of the memory unit. In Figures (a)–(d), X-axis represents sequence of addition.
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