Functionalized Quantum Dot Fluorescent Probes with Dopamine Quinone: Construction and pH Response

doi:10.15541/jim20250169

Abstract

Abstract:

Quantum dots (QDs) have demonstrated significant potential in the field of biological detection due to their excellent photoluminescence properties. As one of the key parameters in regulating physiological functions, pH response with high sensitivity is of great significance. However, conventional pH fluorescent probes are frequently limited by insufficient sensitivity or poor stability. In this work, band gap engineering was used to design and construct a CdSe/CdS/ZnS core-shell structured QD to improve the fluorescence quantum yield and stability. Additionally, the modification with mercaptoethylamine (MEA) and dopamine-isothiocyanate (DA-ITC) results in improved QD fluorescent probe exhibiting a highly sensitive pH response. Experimental results indicate that the amino-protected CdSe/CdS/ZnS QDs possess excellent optical properties. Following modification with DA-ITC, the probe exhibits highly sensitive pH response. The underlying response mechanism is attributed to fluorescence quenching effect of the dopamine quinone (DQ), which is formed by oxidation in surface ligands on the QDs under alkaline conditions. For 1 nmol QDs, when the input amount of DA-ITC is in the range of 4-40 μg/nmol, the fluorescence intensity of the probe reveals a linear decreasing trend with increasing pH from 5.0 to 10.0 (R²>0.90). Notably, when the addition of DA-ITC is set at 20 μg/nmol, the probe demonstrates optimal pH responsiveness (R²=0.9869). Moreover, this probe has good cytocompatibility, allowing for effective application in fluorescence imaging for monitoring of cell pH.

Key words: quantum dot, core-shell structure, pH response, redox

CLC Number:

O649

WANG Zheng, HOU Xiaoqi, LIU Xuanyong. Functionalized Quantum Dot Fluorescent Probes with Dopamine Quinone: Construction and pH Response[J]. Journal of Inorganic Materials, 2026, 41(2): 225-233.

Figures/Tables 13

Fig. 1 Schematic of preparation, micromorphologies and size distributions of QDs (a) Preparation process of QDs; (b-d) TEM images of CdSe QDs (b), CdSe/CdS QDs (c) and CdSe/CdS/ZnS QDs (d),with insets showing size distribution histograms

Fig. 2 Structural characterization, element distribution and optical properties of QDs (a) XPS spectra, (b) XRD patterns, (d) PL and UV-Vis spectra, and (e) transient PL spectra of QDs;(c) EDS mappings of CdSe/CdS/ZnS QDs with inset showing HRTEM image

Fig. 3 Schematic of preparation, characterization and optical properties of QDs-based pH probes (a) Preparation of pH probe; (b) FT-IR spectra of pH probe at different phases; (c) PL spectra and (d) transient PL spectra of QDs before and after MEA ligand exchange; (e) UV-Vis spectra, (f) PL spectra and (g) transient PL spectra of QDs before and after linking DA-ITC (40 μg/nmol)

Fig. 4 Effect of DA-ITC input on optical properties of QDs-based pH probes (a) PL spectra; (b) Variation of PL peak intensity; (c) Transient PL spectra

Fig. 5 Response effects of probes with different DA-ITC input amounts on pH changes

Fig. 6 Cytotoxicity of probe and its pH response effect in the cellular system (a, b) Cytotoxicity of probe to L929 cells (a) and 4T1 cells (b); (c) Fluorescence imaging of probe responses to intracellular pH change

Fig. 7 Effect of GSH on the optical properties of fluorescent probes and pH response mechanism of probes (a, b) Same concentration of GSH and MEA incubated with probe for 30 min: (a) PL spectra and (b) transient PL spectra of probe; (c-e) Different concentration of GSH incubated with probe for 30 min: (c) PL spectra, (d) variation of PL peak intensity and (e) transient PL spectra of probe; (f) Schematic of the mechanism of fluorescence probe response to pH change. Colorful figures are available on website

Table S1 Optical properties of oil-soluble QDs

QDs	The first exciton absorption peak/nm	PL peak/nm	FHWM/nm	PL decay lifetime/ns	χ_R₂
CdSe	558.0	571.5	26.0	/	/
CdSe/CdS	609.5	622.0	25.3	19.35	0.95
CdSe/CdS/ZnS	609.0	625.0	28.4	21.20	1.24

Table S2 Fitting of probe fluorescence response pH under different DA-ITC input amounts

Amount of input/(μg·nmol^-1)	y = b×x + a	R²
0.4	y = -28309x + 587440	0.4777
4	y = -56370x + 670873	0.9097
20	y = -44246x + 522045	0.9869
40	y = -11429x + 141699	0.9667
80	y = -53.148x + 4116.5	0.0249

Fig. S1 Element distribution (a) and EDS line scan image (b) of CdSe/CdS/ZnS quantum dots

Fig. S2 Variation of optical properties during growth of CdS and ZnS layers on CdSe core QDs (a) PL spectra; (b) UV-Vis spectra; (c, d) Transient PL spectra

Fig. S3 Variation of optical properties of probes with different DA-ITC inputs in different pH environments (a, b) 4 μg/nmol; (c, d) 20 μg/nmol; (e, f) 40 μg/nmol; (g, h) 80 μg/nmol

Fig. S4 Fluorescence intensity of probe in intracellular pH fluorescence imaging

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