Visual detection of cysteine and homocysteine

The determination of cysteine and homocysteine levels is of great current interest for the monitoring of desease states. A new colorimetric method for the simultaneous detection of l-cysteine and l-homocysteine has been developed. A fluorescein derivative reacts with the above amino acids, producing their respective thiazolidines resulting in color changes. Interference from other amino acids and proteins is minimal.     

Macrocycle-Derived Functional Xanthenes and Progress Towards Concurrent Detection of Glucose and Fructose

The detection of saccharides in biological media is of great current importance for the monitoring of disease states. We have previously reported that solutions of boronic acid-functionalized macrocycles form acyclic oligomeric materials in situ. The oligomers contain fluorescent xanthene moieties. Current efforts are aimed at modulating the spectroscopic responses of these materials for the analysis of specific sugars. We describe conditions whereby the xanthene boronic acids exhibit high colorimetric fructose selectivity. In contrast, at physiological levels selective glucose monitoring can be achieved via fluorescence. Additionally, we describe a method which exhibits promise for detecting both glucose and fructose at dual wavelengths in the UV-Vis region. Mechanistic rationale for each of these findings is presented.     

Visible light emission in collisions between O5+ ions and He atoms

Visible light emission spectra during collisions between O⁵⁺ ions and He atoms in the range of 200–800 nm at different projectile energies (4.06–5.31 keV-u⁻¹) have been measured. Emission spectra show that there are three channels of excitation in the O⁵⁺-He collision system: (i) single-electron capture into excited states; (ii) double-electron capture into excited states; (iii) direct excitation of target atoms. There are transitions between states with comparably high quantum numbersnl. The absolute emission cross-sections of every spectral line are calculated. The relations of these cross-sections with the energy of the projectiles are studied. Project supported by the National Natural Science Foundation of China and Chinese Association for Atomic and Molecular Dada.     

Label-free capacitive immunosensors for ultra-trace detection based on the increase of immobilized antibodies on silver nanoparticles

Detection of ultra-trace amounts of antigens by label-free capacitive immunosensors was investigated using electrodes modified with silver nanoparticles (AgNPs) that allows for an increase in the amount of immobilized antibodies. The optimal amount of AgNPs that provided the highest immobilization yield was 48 pmol (in 2.0 mL). The performances of immunosensor electrodes for human serum albumin prepared with AgNPs, were compared to electrodes prepared with gold nanoparticles. The two systems provided the same linear range (1.0 × 10⁻¹⁸ to 1.0 × 10⁻¹⁰ M) and detection limit (1.0 × 10⁻¹⁸ M). The system with AgNPs was used to analyze albumin in urine samples and the results agreed well with the immunoturbidimetric assay (P > 0.05). Electrodes modified with AgNPs and appropriate antibodies were tested for their performances to detect analytes of different sizes. For a macromolecule (human serum albumin) the incorporation of AgNPs improved the detection limit from 100 to 1 aM. For small molecules, microcystin-LR and penicillin G, the detection limits were lowered from 100 and 10 fM to 10 and 0.7 fM, respectively. The high sensitivity and very low detection limits are potentially useful for the analysis of toxins or residues present in samples at ultra-trace levels and this method could easily be applied to other affinity pairs.     

Asymmetrical hippocampal connectivity in mesial temporal lobe epilepsy: evidence from resting state fMRI

Background

Recent studies have shown that the human right-hemispheric auditory cortex is particularly sensitive to reduction in sound quality, with an increase in distortion resulting in an amplification of the auditory N1m response measured in the magnetoencephalography (MEG). Here, we examined whether this sensitivity is specific to the processing of acoustic properties of speech or whether it can be observed also in the processing of sounds with a simple spectral structure. We degraded speech stimuli (vowel /a/), complex non-speech stimuli (a composite of five sinusoidals), and sinusoidal tones by decreasing the amplitude resolution of the signal waveform. The amplitude resolution was impoverished by reducing the number of bits to represent the signal samples. Auditory evoked magnetic fields (AEFs) were measured in the left and right hemisphere of sixteen healthy subjects.

Results

We found that the AEF amplitudes increased significantly with stimulus distortion for all stimulus types, which indicates that the right-hemispheric N1m sensitivity is not related exclusively to degradation of acoustic properties of speech. In addition, the P1m and P2m responses were amplified with increasing distortion similarly in both hemispheres. The AEF latencies were not systematically affected by the distortion.

Conclusions

We propose that the increased activity of AEFs reflects cortical processing of acoustic properties common to both speech and non-speech stimuli. More specifically, the enhancement is most likely caused by spectral changes brought about by the decrease of amplitude resolution, in particular the introduction of periodic, signal-dependent distortion to the original sound. Converging evidence suggests that the observed AEF amplification could reflect cortical sensitivity to periodic sounds.