Bi2O3@Bi nanoparticles for ultrasensitive electrochemical determination of thiourea: monitoring towards environmental pollutants

Dual-mode fluorescent and colorimetric sensing of thiourea and aluminum ion in natural water based on CuO nanoparticles

CuO nanoparticles with good water solubility and uniform particle size were successfully prepared. Interestingly, the oxidase-like activity of CuO NPs was continuously enhanced by the addition of thiourea (TU), and the enzyme activity was further enhanced by the addition of aluminum ion (Al3+). By systematically exploring and optimizing the experimental conditions, including the key parameters such as temperature, reaction time, and pH, a fluorescence-colorimetric dual-mode sensing system based on CuO nanoparticles was constructed. The detection range of TU and Al3+ were 1-100 µM and 1-100 µM, respectively, and the selectivity and precision of detection were further improved. In addition, the catalytic mechanism of CuO NPs as oxidase-like catalysts and the specific process in the reaction were investigated. Finally, the nano-sensing system was successfully applied to the analysis of three real environmental samples, namely, tap water, lake water and river water, which provided an effective new strategy for the future development of nano-sensing technology for TU and Al3+.

Hydrangea-like TiO2/Bi2MoO6 porous nanoflowers triggering highly sensitive electrochemical immunosensing to tumor marker

Rapid and sensitive detection of carcinoembryonic antigen (CEA) is of great significance for cancer patients. Here, molybdenum (Mo) was doped into bismuth oxide (Bi2O3) by one-pot hydrothermal method forming porous tremella Bi2MoO6 nanocomposites with a larger specific surface area than the spherical structure. Then, a new kind of hydrangea-like TiO2/Bi2MoO6 porous nanoflowers (NFs) was prepared by doping titanium into Bi2MoO6, where titanium dioxide (TiO2) grew in situ on the surface of Bi2MoO6 nanoparticles (NPs). The hydrangea-like structure provides larger specific surface area, higher electron transfer ability and biocompatibility as well as more active sites conducive to the attachment of anti-carcinoembryonic antigen (anti-CEA) to TiO2/Bi2MoO6 NFs. A novel label-free electrochemical immunosensor was then constructed for the quantitative detection of CEA using TiO2/Bi2MoO6 NFs as sensing platform, showing a good linear relationship with CEA in the concentration range 1.0 pg/mL ~ 1.0 mg/mL and a detection limit of 0.125 pg/mL (S/N = 3). The results achieved with the designed immunosensor are comparable with many existing immunosensors used for the detection of CEA in real samples.

A highly efficient metal oxide incorporated metal organic framework [Nd2O3-MIL(Fe)-88A] for the electrochemical detection of dichlorvos

In this study, a Nd₂O₃@MIL(Fe)-88A composite was prepared through a hydrothermal method and used to detect dichlorvos. The XRD result demonstrated that the prepared sensor is highly crystalline in nature. The affinity of metal oxide and MIL(Fe)-88A could be utilised to overcome low stability and sensitivity owing to their synergistic and electronic effects. Differential pulse voltammetry (DPV) exhibits the electrocatalytic behaviour of Nd₂O₃@MIL(Fe)-88A; it functions at a lower potential at -0.5 to 0.8 V and has a wide linear range of 1-250 nM. It shows a very low detection limit of 0.92 nM with good sensitivity (4.42 mA nM^-1) and selectivity. The developed Nd₂O₃@MIL(Fe)-88A sensor was successfully applied to detect dichlorvos in real analysis. The recovery range calculated for cabbage and orange extracts was 96-97% and 99.5-103.4%, respectively, and RSD% calculated for cabbage and orange extracts was from 1.40 to 3.39% and from 0.64 to 2.26%, respectively.

Fabrication of hierarchical β-Bi2O3/AuAg microspheres for sensitive, selective and rapid detection of environment pollutants by surface-enhanced Raman spectroscopy

In this paper, we report a novel surface-enhanced Raman spectroscopy (SERS) substrate based on hierarchical β-Bi2O3/Au2Ag2 microspheres for rapid, sensitive and selective detection of environment pollutants including o-dianisidine (o-diASD) and Hg2+ in environmental samples. The sheet-like β-Bi2O3 not only provides large specific surface areas for adsorption of molecules and AuAg, but also emerges as semiconductor matrix with chemical enhancement combined with AuAg with electromagnetic enhancement, making promising SERS activity. Particularly, the β-Bi2O3/Au2Ag2 shows high SERS performance for 4-mercaptobenzoic acid and TMB with minimum detectable concentration of 0.1 μg/L with enhancement factor of 3.1 × 107 and 6.3 × 107, respectively. The density functional theory simulations were further adopted to explain the high SERS activity and selectivity for o-diASD and TMB. Finally, the β-Bi2O3/Au2Ag2 was applied to direct detection of o-diASD, and indirect detection of Hg2+ by TMB marking in environmental samples. The linearity range of 0.5-200.0 and 0.2-500.0 μg/L with limit of detection of 0.2 and 0.07 μg/L for o-diASD and Hg2+ ions can be achieved, respectively. This method provides a novel strategy in designing and fabricating SERS substrates with high performance for rapid, sensitive and accurate analysis of environmental pollutants.

A fluorescent probe based on FRET effect between carbon nanodots and gold nanoparticles for sensitive detection of thiourea

Illegal abuse results in the presence of thiourea (TU) in soil, wastewater, and even fruits, which is harmful for the environment and human health. It has urgent practical significance to design an efficient and reliable probe for TU detection. Herein, a sensitive fluorescent probe with off-on response for harmful TU was reported. The probe was designed with fluorescent carbon nanodots (CNDs) and gold nanoparticles (AuNPs) based on fluorescence resonance energy transfer (FRET) effect. Firstly, the CNDs were pre-combined with AuNPs and the fluorescence of CNDs was quenched due to the FRET effect. Upon addition of TU, the fluorescence of CNDs recovered due to the unbinding of CNDs and AuNPs, since the coordination interaction between TU and AuNPs is stronger than the electrostatic interaction among CNDs and AuNPs. Under the optimum parameters, a linear relationship was found between the relative fluorescence intensity of the probe and the concentration of TU in the range of 5.00 × 10^-8-1.00 × 10^-6 M (R² = 0.9958), with the limit of detection (LOD) calculated to be 3.62 × 10^-8 M. This proposed method is easy to operate and has excellent selectivity and sensitivity for TU, which can be effectively applied in environmental water and compound fruit-vegetable juice.

Outlook on bismuth-based photocatalysts for environmental applications: A specific emphasis on Z-scheme mechanisms

Semiconductor photocatalysis is thought to be a viable solution for addressing the growing problem of environmental pollution. Bismuth (Bi) metal oxides can function as a direct plasmonic photocatalyst or cocatalyst to accelerate the photogenerated charge separation and thus improve their photocatalytic activity. Hence, Bi-based photocatalysts have received a lot of attention due to their extensive environmental applications, including pollutant remediation and energy concepts. Massive efforts have been undertaken in the recent decade to find superior Bi-metal oxides (Bi₂XO_6, X = MO, W, or Cr) and to uncover the corresponding photocatalytic reaction mechanism for the degradation of organic contaminants in water. Herein, the unique crystalline and electronic properties and main synthesis methods, as well as the major Bi-Based direct Z-scheme photocatalysts, are timely discussed and summarized in their usage in water treatment. Besides, the impact of Bi₂XO₆ in energy storage devices and solar energy conversion is reviewed as an energy application. Finally, the future development and challenges of Z-scheme-based Bi₂XO₆ photocatalysts are briefly explored, summarized, and forecasted.