The goal of this proposal is to overcome the limitations of current environmental sampling instruments by establishing an entirely new technique that will enable nanoparticles to be collected and concentrated at very high flow rates, so that they can be directly detected using a continuous-flow microfluidic approach coupled with particle sizing analysis. This approach offers unique potential to deliver a more detailed picture of nanoparticle exposure levels while simultaneously providing the ability to respond to sudden environmental changes. First, they will harness microfluidic interfacial fluorescence phenomena they have recently discovered as the basis for an innovative nanoparticle detection approach. Fundamental parameters including sensitivity and specificity will be characterized to establish detection limits for comparison with current-generation instrumentation. Second, they will leverage their extensive expertise in aerosol sampling to build a real-time autonomous wetted wall cyclone (WWC) collector system optimally suited for continuous environmental sampling of nanomaterials. Output from the WWC will be fed into the microfluidic detection component to provide automated on-line detection capability. Collector design for nanoparticle capture will be guided by coordinated computational fluid dynamics simulations and high-speed, highresolution particle image velocimetry measurements to characterize the 3-D flow fields within the WWC. Experiments will focus on TiO2, Al2O3, and SiO2 nanoparticles as model materials.

Intellectual Merit: The primary outcome of this work will be the fundamental engineering knowledge to design a prototype nanoparticle detector system optimized for high-throughput environmental sampling. Additional outcomes include (1) an improved fundamental understanding about adsorptive interfacial complexation effects in microfluidic flows of nanoparticle-laden suspensions; (2) data assessing the sensitivity, selectivity, and limits of detection associated with the microfluidic-based detection system; and (3) a new tool to assess dynamic changes in environmental nanoparticle concentrations within an entire workspace volume, coupled with particle sizing to better assess potential toxicity.

Broader Impacts: The multidisciplinary nature of this work will be leveraged to develop new research experiences and courses that expose both graduate and undergraduate students to areas at the frontier of nanotechnology. Minority recruitment will be particularly emphasized through their involvement with existing NSF REU and SROP programs. They also plan a number of outreach activities to increase societal awareness of nanoparticles and their environmental impact by hosting seminars and open lab access on a regular basis to high school students and teachers. They will also host visiting programs and open lab access for industrial and medical collaborators.

Novelty: The novelty of their proposed concept compared to previous work in the field is twofold. First, it provides a method to sample environmental nanomaterials with throughput high enough to permit continuous analysis. Second, it introduces an entirely new microfluidic-based nanoparticle detection approach that requires relatively simple instrumentation yet is sensitive at low concentrations. Development of this detection method will advance engineering science by providing new fundamental insights about absorptive dye-nanoparticle interactions and their role in governing fluorescence enhancement/quenching of the resulting complexes. More broadly, this work will enable assessment of dynamic changes in environmental nanoparticle concentrations within an entire workspace volume, coupled with particle sizing to better assess potential toxicity?capabilities not available in current generation instruments.

Project Report

Increasingly broad exposure pathways are an unavoidable consequence of the growing prevalence of nanomaterials, posing new and largely unknown health risks. Efforts to assess safe exposure limits and establish correlations with potentially adverse health consequences critically depend on the ability to monitor the concentration of airborne nanomaterials. But current-generation "personal" samplers, while useful in providing coarse assessments of post-inhalation contact, are unable to provide a time-resolved picture of the transport and fate of dispersed nanomaterials. Our research has produced a breakthrough that overcomes these limitations by enabling continuous online quantification and characterization of nanoparticle composition, size, and morphology independent of agglomeration state. This is accomplished by exploiting localized complexation of nanoparticles in suspension triggered by a sharp chemical discontinuity, yielding a signature easily detectable over 4 orders of magnitude in concentration. Our approach uniquely combines ultra-high flow rate sampling (up to > 1,000 L/min) with sensitive detection based on localized fluorescent complexation, permitting sensitive quantitative measurement of nanoparticle concentration (Figure 1). This new capability makes it possible to establish dynamic exposure profiles not readily obtainable using current-generation personal sampling instruments. In addition, this approach offers a versatile analysis tool suitable for online deployment in a host of synthesis and manufacturing settings. Nanomaterial analysis pertinent to quality control and exposure is a timely topic of intense and rapidly growing interest. But a major roadblock continues to be a lack of robust characterization methods capable of providing online real-time analysis. Our work uniquely overcomes these barriers, making it possible for the first time to dynamically quantify changes in composition, size, morphology, and concentration in a format amenable to portable automated operation. We are not aware of any other currently available method offering comparable online characterization of solution-based nanomaterials. Our discovery therefore has potential to fill a significant need as a platform for routine analysis in a highly automated fashion.

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Texas Engineering Experiment Station
College Station
United States
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