Photoluminescent Histidine-Stabilized Gold Nanoclusters as Efficient Sensors for Fast and Easy Visual Detection of Fe Ions in Water Using Paper-Based Portable Platform

Abstract

Herein is presented a novel and efficient portable paper-based sensing platform using paper-incorporated histidine stabilized gold nanoclusters (His-AuNCs), for the sensitive and selective detection of Fe ions from low-volume real water samples based on photoluminescence (PL) quenching. Highly photoluminescent colloidal His-AuNCs are obtained via a novel microwave-assisted method. The His-AuNCs-based sensor reveals a limit of detection (LOD) as low as 0.2 μM and a good selectivity towards Fe ions, in solution. Further, the fabricated portable sensing device based on paper impregnated with His-AuNCs proves to be suitable for the easy detection of hazardous Fe levels from real water samples, under UV light exposure, through evaluating the level of PL quenching on paper. Photographic images are thereafter captured with a smartphone camera and the average blue intensity ratio (I/I0) of the His-AuNCs-paper spots is plotted against [Fe2+] revealing a LOD of 3.2 μM. Moreover, selectivity and competitivity assays performed on paper-based sensor prove that the proposed platform presents high selectivity and accuracy for the detection of Fe ions from water samples. To validate the platform, sensing assays are performed on real water samples from local sources, spiked with 35 μM Fe ions (i.e., Fe2+). The obtained recoveries prove the high sensitivity and accuracy of the proposed His-AuNCs-paper-based sensor pointing towards its applicability as an easy-to-use, fast, quantitative and qualitative sensor suitable for on-site detection of toxic levels of Fe ions in low-volume real water samples.

Dual-emissive solid-state histidine-stabilized gold nanoclusters for applications in white-light generation

“…The use of microwaves significantly shortens the synthesis procedure to only 30 minutes making the synthesis more attractive and less time-consuming than room-temperature approaches which take considerably more time. Additionally, as previously shown, 20 His-AuNCs obtained using microwaves exhibit a four times stronger PL emission, at the same excitation, compared to His-AuNCs obtained at room temperature. Afterwards, the His-AuNCs were purified by centrifugation (6000 rpm, 10 min) using a 10 kDa Satorious centrifugal concentrator (Hettich, Germany) to eliminate the surplus of His and unreduced ions.…”

“…The 475 nm emission band exhibits an excitation shoulder located at 380 nm, while the 520 nm one displays a well-defined excitation peak centered at 440 nm, which are in excellent correlation with the aforementioned results. Regarding UV-vis absorption properties, we have shown in our previous publication 20 that His-AuNCs exhibit two weak absorption bands at 256 and 324 nm, related to the presence of stabilizing His. The absence of a specific surface plasmon resonance band at around 520 nm indicates that the synthesized nanomaterial has nanocluster dimensions, which was further confirmed by TEM.…”

“…The His-AuNCs were synthesized using a novel method recently published. 20 Briefly, His (0.1 M, 3 ml) was mixed with HAuCl 4 (10 mM, 1.5 ml) in a G10 sealable microwave vessel and the mixture was introduced into a microwave reactor, where the probe was irradiated in pulses of 850 W power for 30 minutes at 90 °C and 12 000 rpm. The use of microwaves significantly shortens the synthesis procedure to only 30 minutes making the synthesis more attractive and less time-consuming than room-temperature approaches which take considerably more time.…”