Efficient cyanide sensing using plasmonic Ag/Fe3O4 nanoparticles

Abstract

In the line of our previous studies, we have reported a developed sensitive and selective probe for cyanide detection based on Ag/Fe₃O₄ nanoparticles (NPs) with an extremely low limit of detection at the level of ng per milliliter. Herein, we report the improvement of the easy-to-make magnetic silver nanoparticle-based sensor system for cyanide determination in an extended calibration range with higher selectivity and precision. As far as our knowledge is concerned, the detectable linear range from 1.0 nM to 160 μM (0.026 ng mL^-1 to 4.16 μg mL^-1) of the improved simple highly precise technique represents the widest assay that has been reported so far. The method is based on strong enhancement of scattered light of the plasmonic nanoparticles and simultaneously cyanide fluorescence quenching. Although the fluorescence of cyanide is highly selective and precise, its intensity is poor. On the other hand, the strongly enhanced Rayleigh signal has a low repeatability. We proposed a method to remove the interference and obtained an effective factor that is directly proportional to cyanide concentration utilizing both above signals simultaneously. In this work, Ag/Fe₃O₄ NPs have been synthesized easily using a green preparation method and the NPs were consequently characterized using powder XRD, UV-Vis absorption spectroscopy, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). A combination of absorption, Rayleigh and fluorescence characteristics were used for detection of cyanide in real samples and an overview of recently reported sensors for cyanide was also provided.

Fig. 1. (A) TEM images (B) XRD patterns from the Ag/Fe₃O₄ nanoparticles (red) and Fe₃O₄ (black) and (C) EDX analysis of the nanocomposite.

Fig. 2. (A) XRD patterns for Ag and Fe₃O₄ samples; (B) UV-vis absorption spectra of (a) cyanide, (b) Fe₃O₄ nanoparticles, and (c) Ag/Fe₃O₄ nanocomposite, 1 mg L⁻¹; (C) FTIR spectra for (a) Ag/Fe₃O₄, (b) Fe₃O₄ and (c) Ag samples.

Fig. 3. Rayleigh scattering and fluorescence upon addition of Ag/Fe₃O₄ nanoparticles, [CN⁻] = 4.16 μg mL⁻¹, pH = 8.0, λ_ex = 300 nm (inset: the zoom fluorescence spectra of red star position).

Fig. 4. Effect of nanoparticles concentration on the fluorescence intensity I_F, [CN⁻] = 4.16 μg mL⁻¹, pH = 8.0.

Fig. 5. Calibration curve for NPs sensing. Linear plot of ratiometric Rayleigh at 313 nm versus fluorescence at 400 nm to the concentration of Ag/Fe₃O₄ nanoparticle.

Fig. 6. Effect of pH on ΔI_R and ΔI_F, by addition of 0.03 mg per L nanoparticles.

Fig. 7. Time dependency investigation of Rayleigh scattering and fluorescence of solution containing 3 mg L⁻¹ of cyanide after addition of 0.08 mg L⁻¹ of Ag/Fe₃O₄ nanoparticles, immediately up to 195 min, pH 8.0; inset the closer fluorescence spectra.

Fig. 8. Fluorescence intensity (I_F) monitoring, [CN⁻] = 4.16 μg mL⁻¹, pH 8.0; immediately up to 3 seconds.

Fig. 9. Fluorescence monitoring of cyanide in the presence of more than 1000-fold excess of various species after 10 min, λ_ex = 300 nm, pH 8.0.