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1.
ACS Appl Mater Interfaces ; 14(35): 39976-39984, 2022 Sep 07.
Artículo en Inglés | MEDLINE | ID: mdl-36000715

RESUMEN

Solar cells are essentially minority carrier devices, and it is therefore of central importance to understand the pertinent carrier transport processes. Here, we advanced a transport imaging technique to directly visualize the charge motion and collection in the direction of relevant carrier transport and to understand the cell operation and degradation in state-of-the-art cadmium telluride solar cells. We revealed complex carrier transport profiles in the inhomogeneous polycrystalline thin-film solar cell, with the influence of electric junction, interface, recombination, and material composition. The pristine cell showed a unique dual peak in the carrier transport light intensity decay profile, and the dual peak feature disappeared on a degraded cell after light and heat stressing in the lab. The experiments, together with device modeling, suggested that selenium diffusion plays an important role in carrier transport. The work opens a new forum by which to understand the carrier transport and bridge the gap between atomic/nanometer-scale chemical/structural and submicrometer optoelectronic knowledge.

2.
Sci Rep ; 10(1): 2426, 2020 Feb 12.
Artículo en Inglés | MEDLINE | ID: mdl-32051449

RESUMEN

A general problem for semiconductor applications is that very slow deposition on expensive single-crystal substrates yields high crystalline quality with excellent electro-optical properties, but at prohibitive costs and throughput for many applications. In contrast, rapid deposition on inexpensive substrates or nanocrystalline films yields low costs, but comparatively inferior crystallinity, carrier transport, and recombination. Here, we present methods to deposit single-crystal material at rates 2-3 orders of magnitude faster than state-of-the-art epitaxy with low-cost methods without compromising crystalline or electro-optical quality. For example, single-crystal CdTe and CdZnTe films that would take several days to grow by molecular-beam epitaxy are deposited in 8 minutes by close-spaced sublimation, yet retain the same crystalline quality measured by X-ray diffraction rocking curves. The fast deposition is coupled with effective n- and p-type in-situ doping by In, P, and As. The epitaxy can be extended to nanocrystalline substrates. For example, we recrystallize thin CdTe films on glass to deposit large grains with low defect density. The results provide new research paths for photovoltaics, detectors, infrared imaging, flexible electronics, and other applications.

3.
Sci Rep ; 8(1): 14519, 2018 Sep 28.
Artículo en Inglés | MEDLINE | ID: mdl-30266958

RESUMEN

Thin film materials for photovoltaics such as cadmium telluride (CdTe), copper-indium diselenide-based chalcopyrites (CIGS), and lead iodide-based perovskites offer the potential of lower solar module capital costs and improved performance to microcrystalline silicon. However, for decades understanding and controlling hole and electron concentration in these polycrystalline films has been extremely challenging and limiting. Ionic bonding between constituent atoms often leads to tenacious intrinsic compensating defect chemistries that are difficult to control. Device modeling indicates that increasing CdTe hole density while retaining carrier lifetimes of several nanoseconds can increase solar cell efficiency to 25%. This paper describes in-situ Sb, As, and P doping and post-growth annealing that increases hole density from historic 1014 limits to 1016-1017 cm-3 levels without compromising lifetime in thin polycrystalline CdTe films, which opens paths to advance solar performance and achieve costs below conventional electricity sources.

4.
Phys Rev Lett ; 111(6): 067402, 2013 Aug 09.
Artículo en Inglés | MEDLINE | ID: mdl-23971610

RESUMEN

CdTe is one of the most promising materials for thin-film solar cells. However, further improvement of its performance is hindered by its relatively short minority-carrier lifetime. Combining theoretical calculations and experimental measurements, we find that for both intrinsic CdTe and CdTe solar cell devices, longer minority-carrier lifetimes can be achieved under Cd-rich conditions, in contrast to the previous belief that Te-rich conditions are more beneficial. First-principles calculations suggest that the dominant recombination centers limiting the minority-carrier lifetime are the Te antisite and Te interstitial. Therefore, we propose that to optimize the solar cell performance, extrinsic p-type doping (e.g., N, P, or As substitution on Te sites) in CdTe under Cd-rich conditions should be a good approach to simultaneously increase both the minority-carrier lifetime and hole concentration.

5.
Am J Physiol Gastrointest Liver Physiol ; 300(1): G60-70, 2011 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-21030609

RESUMEN

Gut apical Na(+)-glucose cotransporter 1 (SGLT1) activity is high at the birth and during suckling, thus contributing substantially to neonatal glucose homeostasis. We hypothesize that neonates possess high SGLT1 maximal activity by expressing apical SGLT1 protein along the intestinal crypt-villus axis via unique control mechanisms. Kinetics of SGLT1 activity in apical membrane vesicles, prepared from epithelial cells sequentially isolated along the jejunal crypt-villus axis from neonatal piglets by the distended intestinal sac method, were measured. High levels of maximal SGLT1 uptake activity were shown to exist along the jejunal crypt-villus axis in the piglets. Real-time RT-PCR analyses showed that SGLT1 mRNA abundance was lower (P < 0.05) by 30-35% in crypt cells than in villus cells. There were no significant differences in SGLT1 protein abundances on the jejunal apical membrane among upper villus, middle villus, and crypt cells, consistent with the immunohistochemical staining pattern. Higher abundances (P < 0.05) of total eukaryotic initiation factor 4E (eIF4E) protein and eIE4E-binding protein 1 γ-isoform in contrast to a lower (P < 0.05) abundance of phosphorylated (Pi) eukaryotic elongation factor 2 (eEF2) protein and the eEF2-Pi to total eEF2 abundance ratio suggest higher global protein translational efficiency in the crypt cells than in the upper villus cells. In conclusion, neonates have high intestinal apical SGLT1 uptake activity by abundantly expressing SGLT1 protein in the epithelia and on the apical membrane along the entire crypt-villus axis in association with enhanced protein translational control mechanisms in the crypt cells.


Asunto(s)
Animales Recién Nacidos/metabolismo , Mucosa Intestinal/metabolismo , Yeyuno/metabolismo , Transportador 1 de Sodio-Glucosa/metabolismo , Animales , Mucosa Intestinal/citología , Cinética , Porcinos
6.
Sensors (Basel) ; 9(2): 995-1011, 2009.
Artículo en Inglés | MEDLINE | ID: mdl-22399952

RESUMEN

The thixotropic-like properties of saline/glycerol drops, containing biotinylated capture antibodies, on streptavidin-coated glass slides have been investigated, along with their implications for bacterial detection in a fluorescent microarray immunoassay. The thixotropic-like nature of 60:40 saline-glycerol semisolid droplets (with differing amounts of antibodies) was observed when bacteria were captured, and their presence detected using a fluorescently-labeled antibody. Semisolid, gel-like drops of biotinylated capture antibody became liquefied and moved, and then returned to semisolid state, during the normal immunoassay procedures for bacterial capture and detection. Streaking patterns were observed that indicated thixotropic-like characteristics, and this appeared to have allowed excess biotinylated capture antibody to participate in bacterial capture and detection. When developing a microarray for bacterial detection, this must be considered for optimization. For example, with the appropriate concentration of antibody (in this study, 0.125 ng/nL), spots with increased diameter at the point of contact printing (and almost no streaking) were produced, resulting in a maximal signal. With capture antibody concentrations greater than 0.125 ng/nL, the excess biotinylated capture antibody (i.e., that which was residing in the three-dimensional, semisolid droplet space above the surface) was utilized to capture more bacteria. Similarly, when the immunoassay was performed within a hydrophobic barrier (i.e., without a coverslip), brighter spots with increased signal were observed. In addition, when higher concentrations of cells (∼10(8) cells/mL) were available for capture, the importance of unbound capture antibody in the semisolid droplets became apparent because washing off the excess, unbound biotinylated capture antibody before the immunoassay was performed reduced the signal intensity by nearly 50%. This reduction in signal was not observed with lower concentrations of cells (∼10(6) cells/mL). With increased volumes of capture antibody, abnormal spots were visualized, along with decreased signal intensity, after bacterial detection, indicating that the increased droplet volume detrimentally affected the immunoassay.

7.
Anal Bioanal Chem ; 391(2): 497-506, 2008 May.
Artículo en Inglés | MEDLINE | ID: mdl-18389224

RESUMEN

Intoxication and infection caused by foodborne pathogens are important problems worldwide, and screening tests for multiple pathogens are needed because foods may be contaminated with multiple pathogens and/or toxic metabolites. We developed a 96-well microplate, multiplex antibody microarray method to simultaneously capture and detect Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium (S. typhimurium), as well as a biomolecule (chicken immunoglobulin G or IgG employed as a proteinaceous toxin analog) in a single sample. Microarrayed spots of capture antibodies against the targeted analytes were printed within individual wells of streptavidin-coated polystyrene 96-multiwell microtiter plates and a sandwich assay with fluorescein- or Cy3-labeled reporter antibodies was used for detection. (Printing was achieved with a conventional microarray printing robot that was operated with custom-developed microplate arraying software.) Detection of the IgG was realized from ca. 5 to 25 ng/mL, and detection of E. coli O157:H7 and S. typhimurium was realized from ca. 10(6) to 10(9) and ca. 10(7) to 10(9) cells/mL, respectively. Multiplex detection of the two bacteria and the IgG in buffer and in culture-enriched ground beef filtrate was established with a total assay (including detection) time of ca. 2.5 h. Detection of S. typhimurium was largely unaffected by high concentrations of the other bacteria and IgG as well as the ground beef filtrate, whereas a small decrease in response was observed for E. coli O157:H7. The multiwell plate, multiplex antibody microarray platform developed here demonstrates a powerful approach for high-throughput screening of large numbers of food samples for multiple pathogens and toxins.


Asunto(s)
Escherichia coli O157/aislamiento & purificación , Microbiología de Alimentos , Enfermedades Transmitidas por los Alimentos/microbiología , Inmunoensayo/métodos , Análisis por Matrices de Proteínas/métodos , Salmonella typhimurium/aislamiento & purificación , Animales , Anticuerpos Antibacterianos/química , Escherichia coli O157/inmunología , Colorantes Fluorescentes , Contaminación de Alimentos/análisis , Humanos , Límite de Detección , Carne , Salmonella typhimurium/inmunología , Sensibilidad y Especificidad
8.
Anal Chem ; 78(18): 6601-7, 2006 Sep 15.
Artículo en Inglés | MEDLINE | ID: mdl-16970339

RESUMEN

A sandwich fluorescent immunoassay in a microarray format was used to capture and detect E. coli O157:H7. Here, we explored quantitative aspects, limitations, and capture efficiency of the assay. When biotinylated capture antibodies were used, the signal generated was higher (over 5-fold higher with some cell concentrations) compared to biotinylated protein G-bound capture antibodies. By adjusting the concentration of reporter antibody, a linear fluorescent response was observed from approximately 3.0 x 10(6) to approximately 9.0 x 10(7) cells/mL, and this was in agreement with the number of captured bacteria as determined by fluorescence microscopy. Capture efficiency calculations revealed that, as the number of bacteria presented for capture decreased, capture efficiency increased to near 35%. Optimization experiments, with several combinations of capture and reporter antibodies, demonstrated that the amount of bacteria available for capture (10(6) versus 10(8) cells/mL) affected the optimal combination. The findings presented here indicate that antibody microarrays, when used in sandwich assay format, may be effectively used to capture and detect E. coli O157:H7.


Asunto(s)
Anticuerpos Antibacterianos/química , Escherichia coli O157/aislamiento & purificación , Microbiología de Alimentos , Análisis por Matrices de Proteínas/métodos , Recuento de Colonia Microbiana , Microscopía Fluorescente , Sensibilidad y Especificidad
9.
J Microbiol Methods ; 67(3): 527-33, 2006 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-16935371

RESUMEN

Escherichia coli O157:H7, a major foodborne pathogen, has been associated with numerous cases of foodborne illnesses. Rapid methods have been developed for the screening of this pathogen in foods in order to circumvent timely plate culture techniques. Unfortunately, many rapid methods are presumptive and do not claim to confirm the presence of E. coli O157:H7. The previously developed method, enzyme-linked immunomagnetic chemiluminescence (ELIMCL), has been improved upon to allow for fewer incidences of false positives when used to detect E. coli O157:H7 in the presence of mixed cultures. The key feature of this assay is that it combines the highly selective synergism of both anti-O157 and anti-H7 antibodies in the sandwich immunoassay format. This work presents application of a newly semi-automated version of ELIMCL to the detection of E. coli O157:H7 in pristine buffered saline yielding detection limits of approximately 1 x 10(5) to 1 x 10(6) of live cells/mL. ELIMCL was further demonstrated to detect E. coli O157:H7 inoculated into artificially contaminated ground beef at ca. 400 CFU/g after a 5 h enrichment and about 1.5 h assay time for a total detection time of about 6.5 h. Finally, ELIMCL was compared with USFDA's Bacteriological Analytical Manual method for E. coli O157:H7 in a double-blind study. Using McNemar's treatment, the two methods were determined to be statistically similar for the detection of E. coli O157:H7 in ground beef inoculated with mixed cultures of select bacteria.


Asunto(s)
Técnicas Bacteriológicas , Escherichia coli O157/clasificación , Escherichia coli O157/aislamiento & purificación , Microbiología de Alimentos , Separación Inmunomagnética , Luminiscencia , Carne/microbiología , Sensibilidad y Especificidad , Estados Unidos , United States Food and Drug Administration
10.
JPEN J Parenter Enteral Nutr ; 28(4): 210-22; discussion 222-3, 2004.
Artículo en Inglés | MEDLINE | ID: mdl-15291402

RESUMEN

BACKGROUND: Supplementation of total parenteral nutrition (TPN) with a mixture of short-chain fatty acids (SCFA) enhances intestinal adaptation in the adult rodent model. However, the ability and timing of SCFA to augment adaptation in the neonatal intestine is unknown. Furthermore, the specific SCFA inducing the intestinotrophic effects and underlying regulatory mechanism(s) are unclear. Therefore, we examined the effect of SCFA supplemented TPN on structural aspects of intestinal adaptation and hypothesized that butyrate is the SCFA responsible for these effects. METHODS: Piglets (n = 120) were randomized to (1) control TPN or TPN supplemented with (2) 60 mmol/L SCFA (36 mmol/L acetate, 15 mmol/L propionate and 9 mmol/L butyrate), (3) 9 mmol/L butyrate, or (4) 60 mmol/L butyrate. Within each group, piglets were further randomized to examine acute (4, 12, or 24 hours) and chronic (3 or 7 days) adaptations. Indices of intestinal adaptation, including crypt-villus architecture, proliferation and apoptosis, and concentration of the intestinotrophic peptide, glucagon-like pepide-2 (GLP-2), were measured. RESULTS: Villus height was increased (p < .029) within 4 hours by supplemented TPN treatments. Supplemented TPN treatments increased (p < .037) proliferating cell nuclear antigen expression along the entire intestine. Indicative of an antiapoptotic profile, jejunal Bax:Bcl-w abundance was decreased (p = .033) by both butyrate-supplemented TPN treatments, and ileal abundance was decreased (p = .0002) by all supplemented TPN treatments, regardless of time. Supplemented TPN treatments increased (p = .016) plasma GLP-2 concentration at all time points. CONCLUSIONS: Butyrate is the SCFA responsible for augmenting structural aspects of intestinal adaptations by increasing proliferation and decreasing apoptosis within 4 hours postresection. The intestinotrophic mechanism(s) underlying butyrate's effects may involve GLP-2. Ultimately, butyrate administration may enable an infant with short-bowel syndrome to successfully transition to enteral feedings by maximizing their absorptive area.


Asunto(s)
Adaptación Fisiológica/efectos de los fármacos , Butiratos/farmacología , Intestinos/fisiología , Nutrición Parenteral Total , Péptidos/metabolismo , Síndrome del Intestino Corto/terapia , Animales , Animales Recién Nacidos , Apoptosis/efectos de los fármacos , Butiratos/administración & dosificación , División Celular/efectos de los fármacos , Modelos Animales de Enfermedad , Relación Dosis-Respuesta a Droga , Ácidos Grasos Volátiles/administración & dosificación , Ácidos Grasos Volátiles/farmacología , Péptido 2 Similar al Glucagón , Péptidos Similares al Glucagón , Humanos , Íleon/metabolismo , Íleon/patología , Íleon/fisiología , Íleon/cirugía , Absorción Intestinal/efectos de los fármacos , Intestinos/efectos de los fármacos , Intestinos/cirugía , Yeyuno/metabolismo , Yeyuno/patología , Yeyuno/fisiología , Yeyuno/cirugía , Péptidos/sangre , Distribución Aleatoria , Porcinos
11.
J Nutr ; 133(11): 3717-20, 2003 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-14608102

RESUMEN

The nutritional regulation of intestinal adaptation extends beyond the route of nutrient administration as specific nutrients are known to mediate the adaptive response. Dietary carbohydrates are known to enhance intestinal adaptation in patients with short-bowel syndrome. This review discusses SCFA-induced adaptation in intestinal structure and function in adult rat and neonatal piglet models. Potential mechanisms relate to the salvage of energy as SCFA in the colon, direct mediation of intestinal adaptation by SCFA and stimulated release of glucagon-like peptide-2 (GLP-2) from enteroendocrine L cells by SCFA. Among the produced SCFA, butyrate appears to be responsible for increasing plasma GLP-2 concentration, in addition to the enterotrophic effects. Emerging evidence reveals that physiological concentrations of butyrate acutely upregulate the expression of key enterocyte-associated nutrient transporters. Focused experiments are needed to carefully identify the critical components of intestinal adaptation and yield conclusions regarding the relative contributions of SCFA and GLP-2 during the various phases of this process.


Asunto(s)
Ácidos Grasos Volátiles/fisiología , Intestinos/fisiología , Péptidos/fisiología , Adaptación Fisiológica , Animales , Butiratos/farmacología , Péptido 2 Similar al Glucagón , Péptidos Similares al Glucagón , Transportador de Glucosa de Tipo 2 , Humanos , Proteínas de Transporte de Monosacáridos/genética , Síndrome del Intestino Corto/fisiopatología , Porcinos
12.
J Sci Food Agric ; 80(6): 757-762, 2000 May 01.
Artículo en Inglés | MEDLINE | ID: mdl-29345785

RESUMEN

Comparing amino acid (AA) retention levels in pig carcass to true ileal digestible AA intake provides an estimate of the marginal efficiency of AA utilization. Accurate analysis of AA levels in the carcass samples is critical. However, the standard 24 h of hydrolysis does not always provide maximum AA values. A study was carried out to investigate the effect of hydrolysis time on AA measurements in pig carcass. Correction factors to standardize AA levels to 24 h of hydrolysis were also determined. Ground carcass samples were hydrolysed with 6 mol litre-1 hydrochloric acid (HCl) in a 110 °C oven for nine different time periods. Pre-column derivatization with phenyl isothiocyanate (PITC) was used to determine AA concentrations in all of the samples. Hydrolysis time significantly affected (P < 0.001) AA levels. The highest levels (P > 0.05) of valine, isoleucine, serine, glycine, threonine, alanine, arginine, proline, histidine and phenylalanine were not observed with 24 h hydrolysis. Therefore, correction factors and sequential hydrolysis curves are important for these amino acids. In conclusion, the effect of hydrolysis time should be considered in amino acids analysis. © 2000 Society of Chemical Industry.

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