Pesticide Identification Using Surface-Enhanced Raman Spectroscopy and Density Functional Theory Calculations: From Structural Insights to On-Site Detection.

Pesticides play an important role in conventional agriculture. Yet, their harmful effects on the environment are becoming increasingly apparent. The occurrence of pesticides is hence being monitored worldwide. For fast, easy, yet sensitive identification, surface-enhanced Raman spectroscopy (SERS) is a powerful tool. In this study, a method is introduced that may be amended to in-field detection of pesticides. Gold and silver nanoparticles were synthesized, size-tailored, and characterized. The herbicide paraquat and the fungicide thiram served as model compounds. The preparation yielded reproducible SERS spectra. Using quantum chemical computation, Raman and SERS spectra were calculated and analyzed. The interpretation of vibrational modes in combination with SERS enhancement and attenuation allowed us to identify compound-specific bands. The assignment was interpreted in terms of the orientation of paraquat and thiram on the gold and silver nanoparticle surfaces. Paraquat preferred a co-planar arrangement parallel to the gold nanoparticle surface and a head-on orientation on the silver nanoparticle. For thiram, breaking of the disulfide bond was recognized, such that interaction with the surface occurred via the sulfur atoms. Successful detection of the pesticides after recollection from vegetable leaves demonstrated the method's applicability for pesticide identification.

Green Textile Materials for Surface Enhanced Raman Spectroscopy Identification of Pesticides Using a Raman Handheld Spectrometer for In-Field Detection.

Surface enhanced Raman spectroscopy (SERS) has evolved into a powerful analytical method in food and environmental analytical sciences due to its high sensitivity. Pesticide analysis is a major discipline therein. Using sustainable materials has become increasingly important to adhere to Green Chemistry principles. Hence, the green textiles poly-(L-lactic acid) (PLA) and the mixed fabric polyethylene terephthalate polyamide (PET/PA) were investigated for their applicability as solid supports for gold nanoparticles to yield SERS substrates. Gold nanoparticle solutions and green textile supports were prepared after preparation optimization. Particle size, dispersity, and particle distribution over the textiles were characterized by absorption spectroscopy and transmission electron imaging. The performance of the SERS substrates was tested using the three pesticides imidacloprid, paraquat, and thiram and a handheld Raman spectrometer with a laser wavelength of 785 nm. The resulting SERS spectra possessed an intra-substrate variation of 7-8% in terms of the residual standard deviation. The inter-substrate variations amounted to 15% for PET/PA and to 27% for PLA. Substrate background signals were smaller with PLA but more enhanced through PET/PA. The pesticides could be detected at 1 pg on PET/PA and at 3 ng on PLA. Hence, PET/PA woven textile soaked with gold nanoparticle solution provides green SERS substrates and might prove, in combination with fieldable Raman spectrometers, suitable for in-field analytics for pesticide identification.

How Has Educational Expansion Shaped Social Mobility Trends in the United States?

This contribution provides a long-term assessment of intergenerational social mobility trends in the United States across the 20th and early 21st century and assesses the determinants of those trends. In particular, we study how educational expansion has contributed to the observed changes in mobility opportunities for men across cohorts. Drawing on recently developed decomposition methods, we empirically identify the contribution of each of the multiple channels through which changing rates of educational participation shape mobility trends. We find that a modest but gradual increase in social class mobility can nearly exclusively be ascribed to an interaction known as the compositional effect, according to which the direct influence of social class backgrounds on social class destinations is lower among the growing number of individuals attaining higher levels of education. This dominant role of the compositional effect is also due to the fact that, despite pronounced changes in the distribution of education, class inequality in education has remained stable while class returns to education have shown no consistent trend. Our analyses also provide a cautionary tale about mistaking increasing levels of social class mobility for a general trend towards more fluidity in the United States. The impact of parental education on son's educational and class attainment has grown or remained stable, respectively. Here, the compositional effect pertaining to the direct association between parental education and son's class attainment counteracts a long-term trend of increasing inequality in educational attainment tied to parents' education.