Synthesis of Ti₃C₂T_x/TiO₂ Nanowires for Ascorbic Acid, Dopamine, and Uric Acid Simultaneous Sensing ^†

Abstract

The development of electrochemical sensors with high sensitivity for the simultaneous detection of ascorbic acid (AA), dopamine (DA), and uric acid (UA) is urgently desirable in clinical medicine. However, the challenge lies in achieving simultaneous detection due to their close oxidation potentials. In this work, we present the synthesis of a composite material comprised of in situ-grown TiO₂ nanowires (NWs) on a Ti₃C₂T_x substrate (Ti₃C₂T_x/TiO₂ NWs) through a facile alkali process. By modifying a glassy carbon electrode (GCE) with Ti₃C₂T_x/TiO₂ NWs (Ti₃C₂T_x/TiO₂ NWs/GCE), it showed excellent electrocatalytic activity for the simultaneous detection of AA/DA/UA by regulating the surface functional groups of Ti₃C₂T_x. Remarkably, the Ti₃C₂T_x/TiO₂ NWs/GCE enabled simultaneous detection of AA in the range of 300–1800 μM, DA in the range of 2–33 μM, and UA in the range of 2–33 μM. The limits of detection (LODs) for AA, DA, and UA were estimated as 66.07 μM, 0.023 μM, and 0.011 μM, respectively. The proposed Ti₃C₂T_x/TiO₂ NWs/GCE demonstrated good stability, high selectivity, and reliable reproducibility, making it a promising electrochemical sensor for the detection of AA, DA, and UA. This work offers a new perspective for human health monitoring, paving the way for advancements in this field.

1. Introduction

Ascorbic acid (AA), dopamine (DA), and uric acid (UA) coexist in body fluids, with basal concentrations ranging from 100 to 1400 μM, 0.01 to 1 μM, and 200 to 500 μM, respectively. They are three essential biomolecules coexisting in body fluids that play vital roles in regulating various physiological functions [1]. Fluctuations in the levels of these biomolecules have been linked to various common ailments such as skin rashes, Alzheimer’s disease, Parkinson’s disease, and gout [2,3]. Therefore, the rapid and accurate simultaneous detection of AA, DA, and UA concentrations in body fluids plays a crucial role in disease diagnoses [4,5]. In this work, a composite of TiO₂ nanowires grown in situ on Ti₃C₂T_x (Ti₃C₂T_x/TiO₂ NWs) was synthesized through a simple alkali treatment. By regulating the surface functional groups and incorporating TiO₂, the Ti₃C₂T_x/TiO₂-NW-modified electrode achieved the individual and simultaneous detections of AA, DA, and UA. Furthermore, the proposed Ti₃C₂T_x/TiO₂ NWs/GCE exhibited excellent stability, selectivity, reproducibility, and repeatability.

2. Result and Discussion

2.1. Characterization of Ti₃C₂T_x/TiO₂ NWs

SEM images in Figure 1e–g depict the Ti₃C₂T_x treated in a 6 M KOH solution for 10, 20, and 30 h, respectively. After 10 h of alkaline treatment, only a few NWs can be observed growing between the Ti₃C₂T_x lamellae (Figure 1a). Subsequently, after 20 h of alkali treatment, the number of NWs significantly increases (Figure 1b). Moreover, as shown in Figure 1c, the NWs start to clump together after 30 h of alkali treatment. TEM and high-resolution TEM images in Figure 1d–f display the Ti₃C₂T_x treated in a 6 M KOH solution for 20 h. NWs with lengths ranging from 350 to 450 nm and diameters of 10–35 nm grow on the surfaces and edges of the Ti₃C₂T_x lamellae (Figure 1d). The lattice fringe spacing of the lamellae is determined to be 0.253 nm, which corresponds to the (002) crystal plane of Ti₃C₂T_x (Figure 1e). Additionally, the lattice fringe spacing of the NWs is measured to be 0.352 nm, in alignment with the (101) crystal plane of anatase TiO₂ (Figure 1f) [6].

2.2. Simultaneous Measurement of AA, DA, and UA with DPV

Figure 2 demonstrates the simultaneous detection of AA, DA, and UA with DPV on the Ti₃C₂T_x/TiO₂ NWs/GCE, with a scan rate of 50 mV s⁻¹. Figure 2a exhibits distinct oxidation peak potentials for AA, DA, and UA, measuring 0.18 V, 0.32 V, and 0.59 V, respectively. A linear relationship between the peak currents and concentrations is observed in the range of 300–1800 μM for AA, yielding an R² value of 0.9953 (Figure 2b). Similarly, for DA, multiple linear segments are observed within the concentration ranges of 2–9 μM and 9–33 μM, resulting in R² values of 0.9930 and 0.9943, respectively (Figure 2c). For UA, multiple linear segments are observed within the concentration ranges of 2–7 μM and 7–33 μM, yielding R² values of 0.9860 and 0.9977, respectively (Figure 2d). The LODs for AA, DA, and UA are estimated to be 66.07 μM, 0.023 μM, and 0.011 μM, respectively.

3. Conclusions

In summary, the Ti₃C₂T_x/TiO₂-NW-modified GCE demonstrated the simultaneous detection of AA (300–1800 μM), DA (2–33 μM), and UA (2–33 μM) with LODs of 66.07 μM (AA), 0.023 μM (DA), and 0.011 μM (UA). The surface of Ti₃C₂T_x exhibited neutral properties due to the substitution of hydroxyl groups with fluorine groups after alkali treatment. Moreover, the active surface area of the Ti₃C₂T_x/TiO₂ NWs/GCE (0.39 cm²) was approximately five times larger than that of the bare GCE (0.08 cm²) due to the in situ generation of TiO₂ NWs on Ti₃C₂T_x. The distinct separation of the detection peaks for AA, DA, and UA can be attributed to the enhanced transition of charge carriers at the heterojunctions of Ti₃C₂T_x and TiO₂. Overall, the electrochemical sensor based on Ti₃C₂T_x/TiO₂ NWs exhibits exceptional anti-interference ability, stability, and reliable reproducibility.