Quantitative Point-of-Care Colorimetric Assay Modeling Using a Handheld Colorimeter.

Colorimetric assays typically offer a rapid and convenient method to assess analytes that span healthcare monitoring to water quality testing. However, such tests can only provide qualitative results when employed in resource-limited settings or require bulky and expensive equipment such as lab spectrophotometers to allow quantitative measurements. In this paper, we report on the use of a handheld colorimeter to quantitatively determine the concentration of analytes in a manner that is independent of ambient lighting or initial sample color. The method combines the response of the sensor with first-principles modeling that better describes the nature of the assay compared to linear-in-parameters regression modeling that is typically performed in other studies. This method was successfully demonstrated using a number of colorimetric assays: (1) determination of solution pH using a universal indicator, (2) quantification of the DNase presence using a DNA-gold nanoparticle assay, and (3) quantification of the concentration of the antibiotic tetracycline using a cell-based assay.

Interplay of Energetics and ER Stress Exacerbates Alzheimer's Amyloid-ß (Aß) Toxicity in Yeast.

Alzheimer's disease (AD) is a progressive neurodegeneration. Oligomers of amyloid-ß peptides (Aß) are thought to play a pivotal role in AD pathogenesis, yet the mechanisms involved remain unclear. Two major isoforms of Aß associated with AD are Aß40 and Aß42, the latter being more toxic and prone to form oligomers. Here, we took a systems biology approach to study two humanized yeast AD models which expressed either Aß40 or Aß42 in bioreactor cultures. Strict control of oxygen availability and culture pH, strongly affected chronological lifespan and reduced variations during cell growth. Reduced growth rates and biomass yields were observed upon Aß42 expression, indicating a redirection of energy from growth to maintenance. Quantitative physiology analyses furthermore revealed reduced mitochondrial functionality and ATP generation in Aß42 expressing cells, which matched with observed aberrant mitochondrial structures. Genome-wide expression level analysis showed that Aß42 expression triggered strong ER stress and unfolded protein responses. Equivalent expression of Aß40, however, induced only mild ER stress, which resulted in hardly affected physiology. Using AD yeast models in well-controlled cultures strengthened our understanding on how cells translate different Aß toxicity signals into particular cell fate programs, and further enhance their potential as a discovery platform to identify possible therapies.

Raman and ROA spectra of (-)- and (+)-2-Br-hexahelicene: experimental and DFT studies of a π-conjugated chiral system.

The Raman optical activity (ROA) spectra of both enantiomers of 2-Br-hexahelicene in chloroform solution have been measured in the range 1700-300 cm(-1). Density functional theory (DFT) calculations accurately reproduce the observed features. The most intense ROA features are also the most intense Raman features, in the region 1350-1400 cm(-1), and correspond to the so-called D-modes, which play a major role in coronene and other PAHs (polycyclic aromatic hydrocarbons). Together with a detailed analysis of the normal mode structure, the polarizability tensors for the intense Raman features are investigated and related to the principal characteristics of helicene systems, namely, chirality and π-conjugation. Through electron-phonon coupling analysis, we propose a mechanism that justifies the intense ROA signals.