Suseela Somarajan

EuS nanocrystals: a novel synthesis for the generation of monodisperse nanocrystals with size-dependent optical properties

A novel one-step solvothermal synthesis of stable colloidal EuS nanocrystals (NCs) is reported. The EuS NCs were synthesized in oleylamine directly from europium oleate and diethylammonium diethyldithiocarbamate in the presence of dodecanethiol and phenanthroline. The formation of single crystalline monodisperse EuS NCs, with sizes finely controlled by synthetic conditions, was confirmed by x-ray diffraction and high resolution transmission electron microscopy analysis. The exciton transition of EuS NCs blue-shifts to higher energies with decreasing particle sizes, as revealed by optical absorption and photoluminescence measurements. The feasibility of synthesizing monocrystalline EuS nanorods by solvothermal synthesis was also demonstrated, making them potentially viable materials for device applications.

Diabetic gastroparesis alters the biomagnetic signature of the gastric slow wave.

Gastroparesis is characterized by delayed gastric emptying without mechanical obstruction, but remains difficult to diagnose and distinguish from other gastrointestinal (GI) disorders. Gastroparesis affects the gastric slow wave, but non‐invasive assessment has been limited to the electrogastrogram (EGG), which reliably characterizes temporal dynamics but does not provide spatial information.

Noninvasive biomagnetic detection of intestinal slow wave dysrhythmias in chronic mesenteric ischemia

Chronic mesenteric ischemia (CMI) is a challenging clinical problem that is difficult to diagnose noninvasively. Diagnosis early in the disease process would enable life-saving early surgical intervention. Previous studies established that superconducting quantum interference device (SQUID) magnetometers detect the slow wave changes in the magnetoenterogram (MENG) noninvasively following induction of mesenteric ischemia in animal models. The purpose of this study was to assess functional physiological changes in the intestinal slow wave MENG of patients with chronic mesenteric ischemia. Pre- and postoperative studies were conducted on CMI patients using MENG and intraoperative recordings using invasive serosal electromyograms (EMG). Our preoperative MENG recordings showed that patients with CMI exhibited a significant decrease in intestinal slow wave frequency from 8.9 ± 0.3 cpm preprandial to 7.4 ± 0.1 cpm postprandial (P < 0.01) that was not observed in postoperative recordings (9.3 ± 0.2 cpm preprandial and 9.4 ± 0.4 cpm postprandial, P = 0.86). Intraoperative recording detected multiple frequencies from the ischemic portion of jejunum before revascularization, whereas normal serosal intestinal slow wave frequencies were observed after revascularization. The preoperative MENG data also showed signals with multiple frequencies suggestive of uncoupling and intestinal ischemia similar to intraoperative serosal EMG. Our results showed that multichannel MENG can identify intestinal slow wave dysrhythmias in CMI patients.

Biomagnetic and bioelectric detection of gastric slow wave activity in normal human subjects – a correlation study

We measured gastric slow wave activity simultaneously with a Superconducting Quantum Interference Device (SQUID) magnetometer, mucosal electrodes and cutaneous electrodes in 18 normal human subjects (11 women and 7 men). We processed signals with Fourier spectral analysis and SOBI blind-source separation techniques. We observed a high waveform correlation between the mucosal electromyogram (EMG) and multichannel SQUID magnetogastrogram (MGG). There was a lower waveform correlation between the mucosal EMG and cutaneous electrogastrogram (EGG), but the correlation improved with the application of SOBI. There was also a high correlation between the frequency of the electrical activity recorded in the MGG and in mucosal electrodes (r = 0.97). We concluded that SQUID magnetometers noninvasively record gastric slow wave activity that is highly correlated with the activity recorded by invasive mucosal electrodes.

Noninvasive Biomagnetic Detection of Isolated Ischemic Bowel Segments

The slow wave activity was measured in the magnetoenterogram (MENG) of normal porcine subjects ( N = 5) with segmental intestinal ischemia. The correlation changes in enteric slow wave activity were determined in MENG and serosal electromyograms (EMG). MENG recordings show significant changes in the frequency and power distribution of enteric slow-wave signals during segmental ischemia, and these changes agree with changes observed in the serosal EMG. There was a high degree of correlation between the frequency of the electrical activity recorded in MENG and in serosal EMG (r = 0.97). The percentage of power distributed in brady- and normoenteric frequency ranges exhibited significant segmental ischemic changes. Our results suggest that noninvasive MENG detects ischemic changes in isolated small bowel segments.

Characterization of Electrophysiological Propagation by Multichannel Sensors

Objective: The propagation of electrophysiological activity measured by multichannel devices could have significant clinical implications. Gastric slow waves normally propagate along longitudinal paths that are evident in recordings of serosal potentials and transcutaneous magnetic fields. We employed a realistic model of gastric slow wave activity to simulate the transabdominal magnetogastrogram (MGG) recorded in a multichannel biomagnetometer and to determine characteristics of electrophysiological propagation from MGG measurements. Methods: Using MGG simulations of slow wave sources in a realistic abdomen (both superficial and deep sources) and in a horizontally-layered volume conductor, we compared two analytic methods (second-order blind identification, SOBI and surface current density, SCD) that allow quantitative characterization of slow wave propagation. We also evaluated the performance of the methods with simulated experimental noise. The methods were also validated in an experimental animal model. Results: Mean square errors in position estimates were within 2 cm of the correct position, and average propagation velocities within 2 mm/s of the actual velocities. SOBI propagation analysis outperformed the SCD method for dipoles in the superficial and horizontal layer models with and without additive noise. The SCD method gave better estimates for deep sources, but did not handle additive noise as well as SOBI. Conclusion: SOBI-MGG and SCD-MGG were used to quantify slow wave propagation in a realistic abdomen model of gastric electrical activity. Significance: These methods could be generalized to any propagating electrophysiological activity detected by multichannel sensor arrays.

Effects of body mass index on gastric slow wave: A magnetogastrographic study

We measured gastric slow wave activity simultaneously with magnetogastrogram (MGG), mucosal electromyogram (EMG) and electrogastrogram (EGG) in human subjects with varying body mass index (BMI) before and after a meal. In order to investigate the effect of BMI on gastric slow wave parameters, each subjects BMI was calculated and divided into two groups: subjects with BMI ≤ 27 and BMI > 27. Signals were processed with Fourier spectral analysis and second-order blind identification (SOBI) techniques. Our results showed that increased BMI does not affect signal characteristics such as frequency and amplitude of EMG and MGG. Comparison of the postprandial EGG power, on the other hand, showed a statistically significant reduction in subjects with BMI > 27 compared with BMI ≤ 27. In addition to the frequency and amplitude, the use of SOBI-computed propagation maps from MGG data allowed us to visualize the propagating slow wave and compute the propagation velocity in both BMI groups. No significant change in velocity with increasing BMI or meal was observed in our study. In conclusion, multichannel MGG provides an assessment of frequency, amplitude and propagation velocity of the slow wave in subjects with differing BMI categories and was observed to be independent of BMI.

Tu1487 Progressive Occlusion of Mesenteric Artery Changes Biomagnetic Signature of Intestinal Slow Wave

G A A b st ra ct s research. Oral domperidone has been reported in some cases to prolong the QT interval and predispose to ventricular arrhythmias (Reddymasu et al. Am J Gastro 2007;102:20362045). The aims: 1) To establish an indications and clinical profile of patients receiving domperidone through the limited access protocol 2) to investigate possible side effects of domperidone 3) to analyze ECG reports and the duration of QT intervals. Methods: Study involved a retrospective chart review of 163 patients referred to a single physician at the tertiary GI Motility Center. Patients demographics, GI diagnosis, cardiovascular complain and ECG tracings were obtained. Prolonged QTc were verified if they were longer than 470 ms in females and longer than 450 ms in male patients. Results: Overall 23 out of 163 (13%) patients (15 F; mean age 47, range 18-73) presenting with chief complaints of nausea and vomiting were enrolled in FDA approved protocol and received doses of domperidone ranging from 10 to 30mg QID for at least 6 up to 12 months. 8 (36%) patients were Hispanic, 12 (52%) Caucasian, and 3(12%) African American. A total 16 (60%) of these patients (9F) were diagnosed with GP, 4 females met the criteria for Cyclic Vomiting Syndrome and 3 patients had symptoms of unexplained nausea. 6 (27%) ECG reports showed non-significant sinus arrhythmias, and one male patient had an irregular rhythm. Women had mean heart rates of 82 (range 52-112) and mens average HR was 86 (range 55-105) bpm. Overall the mean value of QTc for all domperidone patients was 427 ms (ranges 383 507 ms). Further analysis of ECGs for females showed, mean QTc duration of 425 (394-507) ms and in males it was 429 (383-469) ms. Two patients (9%), one of each gender, had QTc prolongation above the normal respected value. No patients complained about palpitation or cardiac/ chest pain. Two patients noticed breast discomfort. No other potential adverse events including extra-pyramidal side effects were reported during this investigation. Conclusions:1) Domperidone is legally available in USA under the FDAIND approved protocol and can be prescribed for patients with symptoms of nausea and vomiting related to gastroparesis and other motility disorders 2) No clinically relevant cardiac complaints and ECG changes including QTc prolongations were discovered during this observation 3) Domperidone can be regarded as a safe prokinetic and antiemetic agent.

Characterization of EuS Nanotubes in Quantum Confinement

Europium monochalcogenides of the form EuX (X = O, S, Se, Te) have fascinating optical, magneto optical and magnetic properties. For face-centered cubic EuS, increased Curie temperatures and reversal in the remanent magnetization were observed with decreasing particles sizes, ultimately leading to quantum confinement structures. EuS nanoparticles were synthesized by thermolysis of a molecular single source precursor. Dependent on the synthesis parameters, particles sizes ranging either between 2.0 nm and 10.0 nm (nanocrystalline region) or below 2.0 nm (quantum–confined region). With shrinking particle size, surface strain effects can alter the atomic arrangements and therefore the crystal structure. Since the magnetic properties of EuS are governed by the strongly bound 4f orbital, changes in the atomic arrangement thus leads to modified orbital overlaps between nearest neighbor lattice sites and next-nearest neighbor sites. Consequently, size-dependent optical, magnetic [1, 2], and structural characteristics can been observed. Aberration-corrected STEM analysis revealed the presence of highly crystalline face-centered cubic nanoparticles with dimensions well below 2 nm. Figure 1 shows an annular dark field STEM micrograph with nanocrystals of various sizes within the quantim-confined region. The detection of isolated Eu atoms dispersed on the carbon support film indicates atomic resolution and single atom sensitivity during the STEM experiments. In many areas of the sample, non-crystalline agglomerates of Eu atoms (likely in conjunction with sulfur atoms) were observed [3]. Recently, Harrison et al. synthesized EuS nanotubes with unique optical properties due to unidirectional quantum confinement [4]. SEM, TEM and focused ion-beam microscopy confirmed hollow nanotube morphologies (Figure 2) with wall thickness of the order of 2-5 nm. The rolled-up sheets of EuS were found to be poly-crystalline with grain sizes as small as 10-15 nm. At the time of writing, preliminary data suggest an equilibrium length and diameter of the nanotubes. Furthermore, strain within the sheets seems to cause rupturing of the nanotubes for stress relaxation (cf. Figure 2b). Currently, selected area diffraction and analytical STEM experiments are carried out for more detailed evaluations of atomic and electronic structures as well as local chemistry and oxidation states.

Electrophoretic Deposition of Star Polymer-Europium Chalcogenide Nanocomposite Films

The electrophoretic deposition of polystyrene/divinylbenzene (PS/DVB) star polymer-europium sulphide (EuS) nanocomposite films from a colloidal suspension is reported. Liquid suspension, containing both the PS/DVB star polymer and EuS nanocrystals were prepared by separately injecting dichloromethane (DCM) based solutions of EuS nanocrystals and of the star polymers, respectively, into a stratified liquid combination of hexane and DCM. Scanning electron microscopy illustrates images of the dependence of surface morphology on nanocrystal concentration of the PS/DVB-EuS star polymer film. These polymer-encased nanocrystal films may be a more practical option for the fabrication of magneto-optical thin film devices, such as optical switches, optical isolators, and optical memories.