Fast synthesis of Hcy-modified Au nanoclusters under microwave-assisted irradiation and their response to Cu (II) ions

Figures & data

Scheme 1. The preparation strategy for Hcy-modified AuNCs using the microwave-assisted method.

Figure 1. Emission spectra of Hcy-AuNCs prepared upon various microwave powers and irradiation times. The reference sample was a mixture of HAuCl₄ and Hcy upon no microwave heating.

Table 1. Summarized photophysical parameters of AuNCs synthesized under various microwave powders and irradiation time.

Power, time	λem (nm)	FWHM (nm)	Φ (%)
3 W, 1 min	622	61	10.3
5 W, 1 min	624	63	13.4
7 W, 1 min	626	67	10.1
10 W, 1 min	626	69	7.2
3 W, 2 min	627	63	14.9
5 W, 2 min	624	64	17.1
7 W, 2 min	624	65	10.8
10 W, 2 min	626	64	9.9
3 W, 3 min	625	63	14.4
5 W, 3 min	627	63	15.1
7 W, 3 min	628	64	8.1
10 W, 3 min	627	70	6.6
3 W, 5 min	623	64	11.6
5 W, 5 min	624	65	9.9
7 W, 5 min	630	71	5.5
10 W, 5 min	636	82	2.4
Reference sample	No emission	N/A	N/A

Reference sample was a mixture of HAuCl₄ and Hcy upon no microwave heating.

Figure 2. XPS spectrum (a) and TEM image (b) of the as-synthesized AuNCs sample (5 W/2 min).

Figure 3. DLS (a) and Zeta potential (b) of the as-synthesized AuNCs sample (5 W/2 min).

Figure 4. IR spectra of Hcy and the as-synthesized AuNCs sample (5 W/2 min).

Figure 5. Absorption, excitation, and emission spectra of the as-synthesized AuNCs sample (5 W/2 min).

Figure 6. Emission decay dynamics curves (a) of the as-synthesized AuNCs sample (5 W/2 min) without and with Cu(II) (100 μM). Emission spectra (b) of the as-synthesized AuNCs sample (5 W/2 min) upon increasing Cu(II) concentrations from 0 to 130 μM.

Table 2. Biexponential emissive decay parameters of the AuNCs (5 W/2 min).

AuNCs	τ1 (ns)	A1	τ2 (ns)	A2	τ (ns)	kr (s^–1)	knr (s^–1)
No Cu^2+	522.2	0.1639	115.5	1.1195	277.5	6.16 × 10^5	2.99 × 10^6
With Cu^2+	127.3	0.3803	24.4	0.7432	99.3	6.04 × 10^4	1.00 × 10^7

Scheme 2. A possible sensing/energy competing mechanism of Hcy-AuNCs towards Cu(II).

Figure 7. Stern–Volmer equation (a) of the as-synthesized AuNCs sample (5 W/2 min) upon increasing Cu(II) concentrations from 0 to 130 μM fitted with Formula 4. Emission intensity monitoring of the as-synthesized AuNCs sample (5 W/2 min) when Cu(II) and EDTA are periodically added.

Figure 8. F/F₀ ratios of the as-synthesized AuNCs sample (5 W/2 min) upon competing ions (100 μM). 1 = blank, 2 = Cu²⁺, 3 = AcO^–, 4 = PO₄^–, 5 = SO₄^–, 6 = NO₃^–, 7 = Cl^–, 8 = Br^–, 9 = I^–, 10 = Na⁺, 11 = Mg²⁺, 12 = Ca²⁺, 13 = Zn²⁺, 14 = Cd²⁺, 15 = Co²⁺, 16 = Al³⁺, 17 = Fe³⁺, 18 = Fe²⁺, and 19 = Hg²⁺.

Table 3. Sensing performance comparison between Hcy-modified AuNCs and literature sensing systems.

System	Analyte	Sensitivity region	Linearity	Selectivity	Ref
AuNCs@BSA	Ag^+	0.58–1.30	No	N/A	25
HAS-AuNCs	NOx	0.4–1.8	Yes	Good	26
BSA-SuNCs	Cu^2+	∼2.4	Linear-liked	Limited	27
DHLA-AuNCs	Hg^2+	20–100	Yes	Limited	31
AuNCs	Cu^2+	0.03–1.00	Yes	Good	This work

Table 4. Sensing repeatability of Hcy-modified AuNCs.

Cu^2+ added (μM)	By ICP (μM)	By AuNCs (μM)	Recovery
0	0.001	0.7 ± 0.2	N/A^a
10	9.998	9.8 ± 0.3	98.0%
50	50.003	48.6 ± 0.5	97.2%
100	99.989	96.4 ± 1.2	96.4%
150	149.985	110.7 ± 1.9	73.8%

^aLower than LOD (3.2 μM).

Data availability statement

Data are available upon reasonable request from the corresponding authors.