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Mercury is a highly toxic, bioaccumulative heavy metal that can cause serious health problems even at low concentrations, thus presenting a major threat for the natural water resources. Its high toxicity entails low MCL values (e.g., 2 ppb),[1] requiring at best materials that cannot only selectively detect Hg2+ at trace levels but also effectively remove it. Various such dual functional materials have been developed in the past.[2] However, most of these approaches have limitations with respect to sensitivity and selectivity, show slow responses or require complex instrumentation.
Here we report the development of mesoporous silica materials containing boron-dipyrromethene (BODIPY) probes in their pore systems that allow for the sensitive and selective detection of Hg2+ in water via fluorescence enhancement while at the same time efficiently scavenging the toxic heavy metal. For this purpose, we adopted an earlier strategy[3] and prepared a refined BODIPY probe which was directly adsorbed on the surface of SBA-15-type silica having been functionalized with different organic moieties. Of all the materials tested, SBA-15 expressing propyl chains responded best, allowing for an excellent discrimination against Ag+ and other metals as well as a high sensitivity for Hg2+ with a limit of detection of 1.5 ppb.
The performance of the hybrids with regard to sensing and scavenging was validated by ICP-OES measurements before and after exposure of the materials to Hg2+-containing solutions, allowing retentions of 0.07 g Hg2+ g solid-1. Control studies revealed that while the fluorescent probe is responsible for the very sensitive indication at low Hg2+ concentrations, the majority of the toxic metal ion is scavenged at the walls of the silica material. Current work is directed at the incorporation of these sensor particles into filtration systems for monitoring purposes.
The design of comparatively simple and modularly configurable artificial systems able to communicate through the exchange of chemical messengers is, to the best of our knowledge, an unexplored field. As a proof-of-concept, we present here a family of nanoparticles that have been designed to communicate with one another in a hierarchical manner. The concept involves the use of capped mesoporous silica supports in which the messenger delivered by a first type of gated nanoparticle is used to open a second type of nanoparticle, which delivers another messenger that opens a third group of gated nanoobjects. We believe that the conceptual idea that nanodevices can be designed to communicate with one another may result in novel applications and will boost further advances towards cooperative systems with complex behavior as a result of the communication between simple abiotic individual components.
Set them free: Brightly fluorescent indicators that are loaded into mesoporous silica nanoparticle carriers, capped with bulky antibodies, are released into the lateral flow of a test strip upon analyte arrival. Integration of the system into a rapid, simple flow test with fluorescence readout is applied for the selective and sensitive determination of the presence of triacetone triperoxide (TATP) as a prototype small-molecule analyte (see figure).
A droplet-based microfluidic sensor was developed for the detection of Hg2+ traces in water. The approach uses gated mesoporous nanoparticles loaded with a fluorescent BODIPY dye. The squaraine-based gating mechanism is highly selective for Hg2+ and the indicator release mechanism ensures sensitive detection. The microfluidic system is modular and was assembled from simple PTFE/PFA tubes, while detection was realized with standard optomechanic, optic, and electronic parts. The sensor shows a stable response without memory effects and allows the detection of Hg2+ in water down to 20 ppt.