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- 19 Oct 2012
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The rapid development of socio-economic and industrialization have caused the pollution of the water environment with pesticide residues, heavy metals, and radioactivity, among which heavy metal pollution is of great concern. Among the many sources of heavy metal pollution, Pb2+ is considered to be one of the most hazardous metals. Pb is located in the IVA group of the sixth cycle of the periodic table of chemical elements and is one of the most abundant toxic heavy metals. Pb2+ is widely used in many fields such as lead glass, photovoltaic cells, paints, pigments, chemicals, and lead–acid batteries. Low levels of Pb2+ exposure can cause many adverse health effects. Pb2+ can cause abnormalities in the brain, central nervous system, and intelligence [1,2], which will make it dangerous to work in the environment containing Pb2+ wastewater. The research and establishment of rapid detection methods for Pb2+ are of great significance for the prevention and control of water pollution and occupational safety hazards caused by Pb2+.
A large number of powerful electrochemical [3,4,5], colorimetric [6,7,8], and fluorescent-based [9,10,11,12] Pb2+ monitoring sensors have been developed and applied in the last few decades. Huang et al. reported that the synthesized high-fluorescent gold nanoclusters using protamine as both a reducing and a stabilizing reagent were successfully used as a nanoprobe for the fluorescence detection of Pb2+ [9]. Moreover, MoS2 was synthesized as a nanoprobe by the hydrothermal method to design the ion sensors of Co2+, Cd2+, and Pb2+ for the detection of actual water samples [10]. Although scholars in this field have made these achievements, most of the studies mainly focused on the preparation and detection of sensors in solution form. Solid-state sensors with good portability and stability are more attractive in practical occupational safety application scenarios. Among the various solid-state sensing materials, fluorescent carbon dots (CDs) have received increasing attention in recent years. CDs as new fluorescent carbon nanomaterials with a size of less than 10.0 nm are rich in carboxyl and amino groups on the surface [13]. Since 2004, CDs have been widely used in heavy metal pollution tracking, optical catalysis [14,15], biochemical sensing [16], and drug delivery [17,18] due to their high stability, low toxicity, high water solubility, and good biocompatibility [14]. Recently, the application of CDs has attracted considerable attention in heavy metal pollution tracking, which has not been uncommon for international scholars to study in this direction. Wen et al. prepared multicolor fluorescent CDs with a quantum yield of 24.1% from pigskin and successfully used them for Co2+ ion detection and multicolor cellular imaging [15]. Zong et al. prepared CDs using mesoporous silica spheres as nanoreactors, which were successfully applied as fluorescent probes for the highly sensitive and selective detection of Cu2+ and
Few studies have been conducted to prepare chemical sensors using CDs that can detect Pb2+-contaminated water samples flexibly and efficiently. However, the pollution of waters affected by Pb2+ has become an occupational safety issue of worldwide concern. The water-soluble CDs were prepared by hydrothermal synthesis using typical water pollutant cyanobacteria as a raw material. Based on the burst effect of Pb2+ on the fluorescence of CDs, a new method was established for the rapid detection of Pb2+ with simple operation, low cost, and high sensitivity. Then, the obtained CD fluorescent sensor is applied to occupational safety wearable for the field detection of Pb2+ in actual water samples.
The CD source was derived from cyanobacteria, which salvaged from Taihu Lake (Wuxi, China). Dialysis membranes (2,000 Da; Spectrum labs) were purchased from Sigma-Aldrich (Shanghai, China). Pb(NO3)2 was supplied by Sinopharm Chemical Reagent Co., Ltd.
The procedure for the synthesis and preparation of CDs is depicted in Figure 1. In detail, the raw material was first air-dried for 48 h, oven-dried at 60°C for 48 h, and passed through a 70 mesh. The CDs were synthesized via the hydrothermal method using the obtained powder as the carbon source [22]. The cyanobacteria powder (20 g) was treated in 300 mL of purified water under stirring at room temperature for 15 min. Then the mixture was transferred into a polytetrafluoroethylene-equipped stainless-steel autoclave (500 mL) and heated at 200°C for 8 h. After cooling, the mixture was centrifuged at 6,000 rpm for 20 min, the supernatant was taken for dialysis (2,000 Da) for 48 h to obtain the aqueous solution of carbon quantum dots, and then freeze-dried to obtain solid carbon quantum dots.
Figure 1
Schematic diagram of CD synthesis and preparation procedures.
The size of the obtained CDs was obtained using a high-resolution transmission electron microscope (JEOL JEM 2100F, Japan). Photoluminescence analysis was measured with an F-7000 fluorescence spectrophotometer (Hitachi, Japan).
In order to apply the synthesized fluorescent CDs to practical occupational safety scenarios, we further used them in the preparation of wearable gloves. As a carrier for fluorescent CD chemosensors, the designed wearable glove achieves the anteriority of Pb2+ contamination detection without adding additional burden to the occupants. At the same time, wearable gloves are a safety barrier for occupational personnel to avoid physical exposure to contaminated water. CDs and polydopamine (PDA) mediators are homogeneously mixed together by ultrasound [23]. Meanwhile, we prepared gloves containing polyvinyl acetate (PVA) material on the index fingertips. Briefly, CDs (10 mg) were added into the PDA (10 mL, 1.0 mg/mL) solution. Sequentially, the obtained solution was contacted with the gloves containing PVA material for 30 min at 25°C. Ultimately, the obtained gloves were kept at 40°C in an oven for 10 min. The PDA mediator mixed with CDs is co-soluble with the PVA polymer on the index finger tip of the glove by coating to form a stable layer.
The size and fluorescent properties of CDs are depicted in Figure 2. It appears that CDs are well separated with a diameter ranging from 1.5 to 4.2 nm. As depicted in Figure 2b, the fluorescence properties of the as-prepared CDs were investigated. Fluorescence spectra displayed that the optimal emission wavelength of CDs appeared to be 470 nm via 380 nm excitation, which further states clearly blue fluorescence of cyanobacteria-derived CDs. Noticeably, as the excitation wavelength increased from 300 to 400 nm, the fluorescence intensity of CDs also changed correspondingly. Specifically, when the excitation wavelength is less than 380 nm, the fluorescence intensity of CDs gradually increased, and then decreased with the increase in excitation wavelength. These results indicate that the CDs have typical excitation-dependent emission behavior, which is an optical property related to surface state [24,25,26]. Previous studies have shown that the cyanobacteria-derived CDs contained multiple O- and N-related functional groups (e.g., sp2 C–C/C=C, C–N, C–O, C=O) [27,28], which could be highly related to their fluorescence emission [22].
Figure 2
(a) TEM images of CDs and (b) fluorescence spectra of CDs.
We explored the feasibility of using such CDs (e.g., fluorescence intensity) for Pb2+ detection, and the changes in fluorescence intensity of CDs are shown in Figure 3. As can be seen in Figure 3a, the CD solution without Pb2+ exhibited a strong fluorescence intensity at 470 nm. By contrast, the presence of Pb2+ resulted in a significant decrease in the fluorescence intensity, suggesting that Pb2+ could effectively quench the fluorescence of CDs. Figure 3a demonstrates that fluorescence intensity of CDs at 470 nm gradually decreases with an increased Pb2+ concentration, indicating that the sensing system is sensitive to Pb2+ concentration. This phenomenon evidenced that Pb2+ can be attributed to the possible quenching of the fluorescence of CDs via electron or energy transfer [29,30]. It is clear that the fluorescence intensity of CDs positively correlated with the concentrations of Pb2+ (
Figure 3
(a) The fluorescence spectra of CDs with Pb2+ in the emission wavelength of 470 nm and (b) the fluorescence intensity of CDs in response to Pb2+ (0.0–56 μm).
The mediated coating method was used to obtain wearable gloves, and the specific structure and detection process of the gloves are shown in Figure 4. The tip of the index finger of the wearable glove, the detection area (containing CDs), is off-white at room temperature and emits a uniform dark blue fluorescence when illuminated using a 365 nm UV lamp. When the detection area of the gloves was immersed in water samples containing different Pb2+ concentrations, which showed distinctly different degrees of fluorescence burst effect. When the Pb2+ concentration increased from 0 to 56 μm in the water sample, the detection area of the glove showed a gradual and continuous color change of the fluorescence burst, as shown in Figure 5a. To show the process of naked-eye detection more visually, the color change was marked trajectory in the standard chromaticity coordinate model proposed by International Commission on Illumination (CIE), as shown in Figure 5b. The starting and ending points of the trajectory are the color coordinates of the glove monitoring area when the Pb2+ concentration is 0 and 56 μm.
Figure 4
Schematic diagram of the structure and detection process of wearable gloves.
Figure 5
(a) Effect of visual inspection of pure water, lake water, and seawater by gloves and (b) CIE chromatogram of the burst effect of glove on aqueous Pb2+ solutions of 0–56 μm.
In addition, the feasibility of using gloves was investigated to detect Pb2+ in actual water samples. The water from Taihu Lake, Wuxi, China and the seawater from Beilun Port, Ningbo, China were filtered to remove insoluble substances. The two pretreated actual water samples were divided into seven portions and 0, 9.00, 18.00, 27.00, 36.00, 45.00, and 56.00 μm of Pb2+ were added into water samples, respectively. It was tested that the fluorescence color change pattern of the wearable gloves was almost the same between the actual water sample and the pure water sample for the same concentration of Pb2+, as shown in Figure 5a. This demonstrates the suitability of our wearable gloves for visual detection of Pb2+ in real water samples without the need for complex pretreatment processes. The designed wearable gloves are highly practical for real-time Pb2+ detection in occupational scenario scenes. In addition, the prepared gloves can be put on and taken off and operated professionally as easily as untreated gloves. Their functionalization did not place an additional burden on the wearer. The fluorescence intensity of the glove test area remained essentially unchanged for 1 month, showing good stability in actual use and storage. When the fluorescence is quenched by Pb2+ in contaminated water, the gloves cannot be recovered and reused. Considering the value of gloves in practical application scenarios and the possible cost in mass production, it is considered acceptable as a disposable product after reaction triggering. Objective tests show that the applicability to real water samples and stability of gloves have reached high practical application requirements.
Working in occupational environments with safety risks for long time can cause anxiety. Occupational anxiety can have a serious negative impact on employees’ health and productivity. The wearable gloves are designed to reduce safety risks by enhancing the active hazard awareness of professionals through the front of the Pb2+ water contamination detection window. This promises to be an effective way to alleviate employees’ feelings of occupational anxiety.
To explore and enlighten the positive value of similar occupational safety wearables on users’ occupational anxiety and mental health, we invited eight people engaged in landscape water cleaning, aquatic salvage, and domestic wastewater treatment to conduct a subjective test of occupational anxiety. Considering the uncertainty and inconsistency in the knowledge status of Pb2+ water pollution among the eight participants, we first provided them with relevant scientific knowledge. Then, the participants had a complete understanding of the used method, working mechanism, and testing effect of the wearable gloves, and experienced the use of the wearable glove design prototype. Finally, participants used a 0–100% scale to record their feelings of occupational anxiety while working with and without our wearable gloves: 0% means no anxiety at all and 100% means the anxiety is at their tolerance limit. The results of the test are shown in Table 1. Eight participants experienced a 57.42% reduction in occupational anxiety when using the wearable gloves compared to when they were not using them. The subjective test proves that the designed gloves can effectively help the water workers improve their occupational safety and reduce their anxiety. Even if there are no target pollutants that harm workers in the occupational environment, the smart wearable with powerful functions and low additional burden can also provide effective practical help to the risk occupational workers in terms of occupational mental health.
Results of subjective tests of occupational anxiety
| Participant number | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | Average value |
|---|---|---|---|---|---|---|---|---|---|
| Pre-use anxiety (%) | 80 | 60 | 40 | 80 | 55 | 42 | 45 | 70 | 59.00 |
| Post-use anxiety (%) | 18 | 25 | 22 | 40 | 28 | 8 | 30 | 30 | 25.13 |
| Anxiety reduction rate (%) | 77.50 | 58.33 | 45.00 | 50.00 | 49.09 | 80.95 | 33.33 | 57.14 | 57.42 |
We designed and prepared a novel CD fluorescent Pb2+ chemical sensor by hydrothermal synthesis using local water pollutant, cyanobacteria from Taihu Lake. The design of the sensor relies on a fluorescence burst chemical reaction between the fluorescent CDs and Pb2+ to induce a “dark blue to light blue” color change visible to the naked eye under UV light. We innovated the designed sensor to wearable sensing gloves for water occupational safety scenarios. The wearable gloves we have designed are portable, highly sensitive, and easily and effectively detect Pb2+ even in complex actual water use. The gloves can be used in water work scenarios where there is a risk of Pb2+ contamination, such as landscaped waters requiring maintenance cleaning, domestic wastewater areas requiring treatment, and production wastewater areas requiring salvage. Professionals can quickly and directly identify Pb2+-contaminated water samples with wearable sensing gloves. It is notable that this wearable glove with an integrated fluorescent CD sensor not only enhances the safety of occupational personnel through the front contaminated water sample detection window but also shows potential in reducing occupational anxiety in tests. In the objective and subjective tests, the designed gloves show high theoretical value and practical operability in the face of water pollution occupational safety and occupational mental health problems. We hope that this study can inspire the development of more robust and low additional burden detection devices in other integrated pollution environments.
Figure 1
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Figure 5
Results of subjective tests of occupational anxiety
| Participant number | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | Average value |
|---|---|---|---|---|---|---|---|---|---|
| Pre-use anxiety (%) | 80 | 60 | 40 | 80 | 55 | 42 | 45 | 70 | 59.00 |
| Post-use anxiety (%) | 18 | 25 | 22 | 40 | 28 | 8 | 30 | 30 | 25.13 |
| Anxiety reduction rate (%) | 77.50 | 58.33 | 45.00 | 50.00 | 49.09 | 80.95 | 33.33 | 57.14 | 57.42 |
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