Bisphenol A sorption on commercial polyvinyl chloride microplastics: Effects of UV-aging, biofilm colonization and additives on plastic behaviour in the environment.

Chemical additives are important components in commercial microplastics and their leaching behaviour has been widely studied. However, little is known about the potential effect of additives on the adsorption/desorption behaviour of pollutants on microplastics and their subsequent role as vectors for pollutant transport in the environment. In this study, two types of commercial polyvinyl chloride (PVC1 and PVC2) microplastics were aged by UV irradiation and biotic modification via biofilm colonization to investigate the adsorption and desorption behaviour of bisphenol A (BPA). Surface cracks and new functional groups (e.g., O-H) were found on PVC1 after UV irradiation, which increased available adsorption sites and enhanced H‒bonding interaction, resulting in an adsorption capacity increase from 1.28 µg/L to 1.85 µg/L. However, the adsorption and desorption capacity not showed significant changes for PVC2, which might be related to the few characteristic changes after UV aging with the protection of light stabilizers and antioxidants. The adsorption capacity ranged from 1.28 µg/L to 2.06 µg/L for PVC1 and PVC2 microplastics, and increased to 1.62 µg/L-2.95 µg/L after colonization by biofilms. The increased adsorption ability might be related to the N-H functional group, amide groups generated by microorganisms enhancing the affinity for BPA. The opposite effect was observed for desorption. Plasticizers can be metabolized during biofilm formation processes and might play an important role in microorganism colonization. In addition, antioxidants and UV stabilizers might also indirectly influence the colonization of microorganisms' on microplastics by controlling the degree to which PVC microplastics age under UV. The amount of biomass loading on the microplastics would further alter the adsorption/desorption behaviour of contaminants. This study provides important new insights into the evaluation of the fate of plastic particles in natural environments.

Short-term mass loads of per- and polyfluoroalkyl substances in a wastewater treatment plant from South China.

Wastewater treatment plants (WWTPs) are one of the most important sources and sinks for per- and polyfluoroalkyl substances (PFAS). However, limited studies have evaluated short-term temporal variability of PFAS in WWTPs, particularly for their intra-day variations. For this purpose, a time-composite sampling campaign was carried out at a WWTP influent from South China for 1 week. Five out of ten PFAS were found in the influent, i.e., perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorobutane sulfonic acid (PFBS), and perfluorooctanesulfonic acid (PFOS). PFOA was the most domain PFAS whereas PFOS was detected occasionally, which might be associated with the prohibition of PFOS use in China. For the first time, we observed significant intra-day fluctuations in mass fluxes for PFOS. Different from a morning peak of pharmaceuticals reported previously, PFOS mass loads fluctuated sharply at noon and night on the weekdays. Furthermore, the mass fluxes of PFOA on the weekend were significantly elevated. For the other PFAS detected, no significant diurnal variations in mass loads were identified. Correlation analysis indicated that domestic activities (e.g., home cleaning) are likely to be the major source of these perfluorocarboxylic acids especially PFOA. In addition, flow fluxes had little effects on these PFAS mass load. These results can aid in future sampling campaigns and optimizing removal strategies for PFAS in wastewater.

In Situ Insight into the Availability and Desorption Kinetics of Per- and Polyfluoroalkyl Substances in Soils with Diffusive Gradients in Thin Films.

The physicochemical exchange dynamics between the solid and solution phases of per- and polyfluoroalkyl substances (PFAS) in soils needs to be better understood. This study employed an in situ tool, diffusive gradients in thin films (DGT), to understand the distribution and exchange kinetics of five typical PFAS in four soils. Results show a nonlinear relationship between the PFAS masses in DGT and time, implying that PFAS were partially supplied by the solid phase in all of the soils. A dynamic model DGT-induced fluxes in soils/sediments (DIFS) was used to interpret the results and derive the distribution coefficients for the labile fraction (Kdl), response time (tc), and adsorption/desorption rates (k1 and k-1). The larger labile pool size (indicated by Kdl) for the longer chain PFAS implies their higher potential availability. The shorter chain PFAS tend to have a larger tc and relatively smaller k-1, implying that the release of these PFAS in soils might be kinetically limited but not for more hydrophobic compounds, such as perfluorooctanesulfonic acid (PFOS), although soil properties might play an important role. Kdl ultimately controls the PFAS availability in soils, while the PFAS release from soils might be kinetically constrained (which may also hold for biota uptake), particularly for more hydrophilic PFAS.

In situ measurement of an emerging persistent, mobile and toxic (PMT) substance - Melamine and related triazines in waters by diffusive gradient in thin-films.

Melamine has received increasing public attention as a persistent, mobile and toxic (PMT) substance. To better assess environmental exposure and risks of melamine and related triazines (cyromazine, ammeline, and atrazine), a new passive sampling method based on the diffusive gradients in thin films (DGT) technique has been developed and validated in this study. The studied triazines were adsorbed quickly and strongly by the selected mixed cation exchange (MCX) binding gels. This MCX-DGT can linearly accumulate these chemicals over at least 5 days, with neither significant individual influence from pH (6-8), ionic strength (0.01-0.5 M) or dissolved organic matter (0-10 M), or interaction effects. Field applications in Southern China showed that DGT performed well in both sewage treatment plant (STP) and river samples. Melamine was found to be the dominant triazine with the concentrations at µg·L-1 in the STP and receiving river. Surprisingly, much higher concentration of melanine was found in the STP effluent than influent, and appeared to be some of the highest concentrations reported in STPs worldwide to date. Comparable melamine and atrazine concentraions in the STP effluent and receiving river suggested other sources to the river. The MCX-DGT sampler developed here was demonstrated to be reliable and robust for measuring the triazines in waters, and is promising as an in situ tool in understanding the occurrence, sources, and fate of the emerging PMT substances in aquatic environment.

Reversible Ratiometric Probe Combined with the Time-Gated Method for Accurate In Vivo Gastrointestinal pH Sensing.

Fluorescence sensing has the advantages of being real time, noninvasive, and convenient and having a low impact on the original environment for in vivo detection. Here, a reversible time-gated ratiometric in vivo detection method that could eliminate the interferences from probe amount, photon scattering, and absorption is proposed. Correspondingly, the composite probe must be able to reversibly respond to changes in the microenvironment and emit two luminescence signals at the same working wavelength but different lifetimes. Benefitting from the reversible detection mechanism, the probes could be used to monitor a dynamic biological process and the ratio signal value could be determined only by the concentration of analytes, independent of the probe concentration. Furthermore, benefitting from the same working wavelength, the read-out errors from photon absorption and scattering could be minimized. This method is very suitable for in vivo detection in which the probe distribution and depth are unknown and variable. As a typical model, different pH values in the gastrointestinal area and pH changes caused by drugs and fasting are successfully monitored.

Near-Infrared Lanthanide-Doped Nanoparticles for a Low Interference Lateral Flow Immunoassay Test.

The lateral flow immunoassay test (LFT), as a method of a point of care test, is widely used in disease diagnosis, food security, and environment observation due to its portability and testing rapidity. A fluorescence lateral flow immunoassay was developed recently to enhance the sensitivity and accuracy of the LFT. However, for most fluorescence reporters, their emission and excitation wavelengths are located in the ultraviolet or visible region. Serum or whole blood significantly absorbs and scatters light of this region, and this will result in background signal interference. In this study, we replace traditional fluorescence reporters with near-infrared lanthanide-doped nanoparticles (NIR-RENPs) to establish a NIR-LFT platform. Blood and other biological samples scatter and absorb less near-infrared light than visible light, and the autofluorescence of biological samples is rarely located in this region. Therefore, using NIR light as a signal can diminish the interference of background noise and suffer from less signal attenuation. In addition, compared with commonly used NIR organic dye, NIR-RENPs have better stability. It is promising that lateral flow immunoassays based on NIR lanthanide-doped nanoparticles are able to acquire a lower detection limit and better accuracy, and they are more suitable for application in commercial settings.

Yb-Based Nanoparticles with the Same Excitation and Emission Wavelength for Sensitive in Vivo Biodetection.

Near-infrared luminescent emission has been widely used as a signal for biological detection with its high spatial resolution and fast response. Rare-earthdoped nanoparticle-dye composites have diverse advantages of a wide operation wavelength and remarkable light stability, while the application is limited by the low luminescence quantum yield of rare-earth nanoparticles. Hence, in this work, we use a singly Yb doped nanoparticle that has strong luminescence emission at 975 nm under excitation at the same wavelength as an energy donor to construct the detection system. An inner filter pair, composed of core-shell nanophosphor NaYF4/20%Yb@NaYF4 (1:2) nanocrystals (csYb) as a luminescent beacon and ClO--responsive cyanine dye Cy890 as a filtering agent, was designed as a model. With a time-gated detection mode, the nanocomposites realize the detection limit at 0.55 ppb as demonstrated in a ClO- detection trial. The csYb&Cy890 nanocomposites can also monitor ClO- by luminescence signals in both living cells and mice models.

3D-Flower-Like Copper Sulfide Nanoflake-Decorated Carbon Nanofragments-Modified Glassy Carbon Electrodes for Simultaneous Electrocatalytic Sensing of Co-existing Hydroquinone and Catechol.

A copper sulfide nanoflakes-decorated carbon nanofragments-modified glassy carbon electrode (CuS-CNF/GCE) was fabricated for the electrocatalytic differentiation and determination of hydroquinone (HQ) and catechol (CC). The physicochemical properties of the CuS-CNF were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. The electrocatalytic determination of HQ and CC over the CuS-CNF/GCE was evaluated by cyclic voltammetry and differential pulse voltammetry. An excellent detection limit and sensitivity of the CuS-CNF/GCE are obtained (0.293 µM and 0.259 µM) with a sensitivity of 184 nA µM-1 cm-2 and 208 nA µM-1 cm-2 (S/N=3) for HQ and CC, respectively. In addition, the CuS-CNF/GCE shows a selective identification of HQ and CC over potential interfering metal ions (Zn2+, Na+, K+, NO3-, SO42-, Cl-) and organic compounds (ascorbic acid, glucose), and a satisfactory recovery is also obtained in the spiked water samples. These results suggest that the CuS-CNF/GCE can be used as an efficient electrochemical sensor for the simultaneous determination of co-existing environmental pollutants such as HQ and CC in water environments with high selectivity and acceptable reproducibility.

Fluorescence lifetime imaging of upper gastrointestinal pH in vivo with a lanthanide based near-infrared τ probe.

Time-resolved fluorescence lifetime imaging (FLIM) in the near-infrared region of 900-1700 nm not only allows a deep tissue penetration depth but also offers the unique benefit of the quantitative visualization of molecular events in vivo and is independent of local luminescence intensity and fluorophore concentration. Herein, we report the design of a wide-range pH sensitive molecular probe based on Yb3+ porphyrinate. The Yb3+ probe shows increasing NIR emission and lifetime with pK a values of ca. 6.6 from pH 9.0 and 5.0 and also displays an elongated lifetime from ca. 135 to 170 µs at lower pH values (5.0-1.0) due to aggregation and reduced exposure to water at low pH values. Importantly, the probe is able to monitor a wide range of in vivo gastrointestinal pH values in mice models and the potential applications in imaging-guided gastrointestinal diagnostics and therapeutics were revealed. This study shows that lifetime contrast is important for preclinical imaging; lanthanide complexes could be successfully used in the design of stimuli-responsive NIR τ probes for advanced in vivo imaging.

Time-Gated Ratiometric Detection with the Same Working Wavelength To Minimize the Interferences from Photon Attenuation for Accurate in Vivo Detection.

Luminescence imaging, exhibiting noninvasive, sensitive, rapid, and versatile properties, plays an important role in biomedical applications. It is usually unsuitable for direct biodetection, because the detected luminescence intensity can be influenced by various factors such as the luminescent substance concentration, the depth of the luminescent substance in the organism, etc. Ratiometric imaging may eliminate the interference due to the luminescent substance concentration on the working signal. However, the conventional ratiometric imaging mode has a limited capacity for in vivo signal acquisition and fidelity due to the highly variable and wavelength-dependent scattering and absorption process in biotissue. In this work, we demonstrate a general imaging mode in which two signals with the same working wavelength are used to perform ratiometric sensing ignoring the depth of the luminescent substance in the organism. Dual-channel decoding is achieved by time-gated imaging technology, in which the signals from lanthanide ions and fluorescent dyes are distinguished by their different luminescent lifetimes. The ratiometric signal is proven to be nonsensitive to the detection depth and excitation power densities; thus, we could utilize the working curve measured in vitro to determine the amount of target substance (hypochlorous acid) in vivo.

An efficient dye-sensitized NIR emissive lanthanide nanomaterial and its application in fluorescence-guided peritumoral lymph node dissection.

The luminescence intensity of near-infrared (NIR) emitting lanthanide nanoparticles (LnNPs) is usually limited, owing to their small absorption cross section. Although dye sensitization has been proven to be an effective way to improve the luminescence intensity of LnNPs, the sensitization effect is fairly limited, owing to the simplicity of the sensitizers used and the complexity of the energy transfer process, typically involving three steps. In this study, a more efficient sensitizer (Cy7) was chosen to replace a commonly used one (ICG) and the energy transfer process was also optimized through using Yb3+ ions as emitter ions and Nd3+ ions as intermediate ions. With Cy7 as a sensitizer, the sensitization effect was assessed to be better than with ICG, owing to the higher quantum yield of Cy7. Meanwhile, the Cy7-sensitized NIR lanthanide nanomaterial was proven to be good for deep tissue penetration and low-power excitation bioimaging. Furthermore, the highly-enhanced NIR signal was successfully used in blood vessel imaging and fluorescence-guided peritumoral lymph node dissection in a mouse model.

Revisiting the optimized doping ratio in core/shell nanostructured upconversion particles.

The development of rare-earth doped upconversion nanoparticles (RE-UCNPs) in various applications is fuelling the demand for nanoparticles with highly enhanced upconversion luminescence (UCL). Although the core/shell structure is proved to enhance the UCL effectively, there is still plenty of room to further improve the UCL by optimizing the doping ratio of the materials. In this article, a general strategy is demonstrated to achieve highly-enhanced visible UCL in core/shell nanostructured NaREF4 by increasing the doping ratio of Yb3+ in the core region. The energy transfer from RE-UCNPs to surface quenching sites through Yb3+-Yb3+ energy migration is demonstrated to be the main reason for restricting the doping ratio of Yb3+. Notable UCL enhancement (ca. 15 times) of core/shell structured α-NaYF4:Yb,Er@CaF2 nanoparticles is observed by increasing the concentration of Yb3+ to 98 mol%. The highly-enhanced visible UCL signal is used to guide the lymphatic vessel resection with the naked eye.