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Lin CH, Lee GB, Fu LM, Chen SH. Integrated optical-fiber capillary electrophoresis microchips with novel spin-on-glass surface modification. Biosens Bioelectron 2004; 20:83-90. [PMID: 15142580 DOI: 10.1016/j.bios.2003.09.011] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2003] [Accepted: 09/24/2003] [Indexed: 11/20/2022]
Abstract
This paper presents a novel micro-capillary electrophoresis (CE) chip with embedded optical fibers for the on-line detection of DNA samples. The optical fibers are pre-etched and then inserted directly into fiber channels incorporated within low-cost soda-lime glass substrates. The embedded optical fibers are precisely aligned with the microfluidic channels such that the induced fluorescence signals from labeled bio-samples can be detected. This arrangement avoids the requirement for delicate optical alignment procedures and equipment. Surface modification of the CE channels is accomplished by means of a simple and reliable organic-based spin-on-glass (SOG) method. The zeta potential distribution and the corresponding electroosmotic mobility of the fluid are simulated numerically for the modified and non-modified channel surfaces, and then both sets of results are verified experimentally. The present results indicate that the value of the zeta potential for a surface with an SOG coating is 19.3 times smaller than that of an untreated surface. A phiX-174 DNA marker fluid is used to evaluate the injection and separation performance of the developed micro-CE device. Furthermore, the long-term stability of the SOG-coated surface is also investigated. The experimental data reveal that the microchip device is capable of providing highly efficient separations of bio-molecules, and that the SOG layer retains its low zeta potential characteristics for at least 45 days. The present results confirm the effectiveness of the proposed micro-CE chip in performing the on-line detection of DNA samples, and indicate that the SOG process represents a simple and reliable solution for the surface modification of glass-based microchannels.
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178
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Fu LM, Yang RJ, Lin CH, Pan YJ, Lee GB. Electrokinetically driven micro flow cytometers with integrated fiber optics for on-line cell/particle detection. Anal Chim Acta 2004. [DOI: 10.1016/j.aca.2003.10.028] [Citation(s) in RCA: 113] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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179
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Sung WC, Huang SY, Liao PC, Lee GB, Li CW, Chen SH. Poly(dimethylsiloxane)-based microfluidic device with electrospray ionization-mass spectrometry interface for protein identification. Electrophoresis 2003; 24:3648-54. [PMID: 14613189 DOI: 10.1002/elps.200305623] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
An easy method to fabricate poly(dimethylsiloxane) (PDMS)-based microfluidic chips for protein identification by tandem mass spectrometry is presented. This microchip has typical electrophoretic microchannels, a flow-through sampling inlet, and a sheathless nanoelectrospray ionization (ESI) interface. The surface of the microchannel was modified with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and the generated electroosmotic flow under acidic buffer condition used for the separation was found to be more stable compared to that generated by the microchannel without modification. The feasibility of the device for flow-through sampling, separation, and ESI-MS/MS analysis was demonstrated by the analysis of a standard mixture composed of three tryptic peptides. Results show that four peaks corresponding to three peptide standards and acetylated products of the standard peptide were well resolved and the deduced sequences were consistent with those expected. Furthermore, the compatibility of this device with other miniaturized devices to integrate the whole process was also explored by connecting a miniaturized enzymatic digestion cartridge and a desalting cartridge in series to the sampling inlet of the microchip for the identification of a model protein, beta-casein.
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180
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Fu LM, Yang RJ, Lee GB, Pan YJ. Multiple injection techniques for microfluidic sample handling. Electrophoresis 2003; 24:3026-32. [PMID: 12973806 DOI: 10.1002/elps.200305528] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
This paper presents an experimental and numerical investigation into electrokinetic focusing flow injection for bioanalytical applications on 1 x N (i.e., 1 sample inlet port and N outlet ports) and M x N (i.e., M sample inlet ports and N outlet ports) microfluidic chips. A novel device is presented which integrates two important microfluidic phenomena, namely electrokinetic focusing and valveless flow switching within multiported microchannels. The study proposes a voltage control model which achieves electrokinetic focusing in a prefocusing sample injection system and which allows the volume of the sample to be controlled. Using the developed methods, the study shows how the sample may be prefocused electrokinetically into a narrow stream prior to being injected continuously into specified outlet ports. The microfluidic chips presented within this paper possess an exciting potential for use in a variety of techniques, including high-throughput chemical analysis, cell fusion, fraction collection, fast sample mixing, and many other applications within the micrototalanalysis systems field.
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181
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Fu LM, Yang RJ, Lee GB. Electrokinetic focusing injection methods on microfluidic devices. Anal Chem 2003; 75:1905-10. [PMID: 12713049 DOI: 10.1021/ac020741d] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This paper presents an experimental and numerical investigation into electrokinetic focusing injection on microfluidic chips. The valving characteristics on microfluidic devices are controlled through appropriate manipulations of the electric potential strengths during the sample loading and dispensing steps. The present study also addresses the design and testing of various injection systems used to deliver a sample plug. A novel double-cross injection microfluidic chip is fabricated, which employs electrokinetic focusing to deliver sample plugs of variable volume. The proposed design combines several functions of traditional sample plug injection systems on a single microfluidic chip. The injection technique uses an unique sequence of loading steps with different electric potential distributions and magnitudes within the various channels to effectuate a virtual valve.
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Fu LM, Yang RJ, Lee GB, Liu HH. Electrokinetic injection techniques in microfluidic chips. Anal Chem 2002; 74:5084-91. [PMID: 12380834 DOI: 10.1021/ac025821w] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The separation efficiency of a microfluidic chip is influenced to a significant degree by the flow field conditions within the injection microchannel. Therefore, an understanding of the physics of the flow within this channel is beneficial in the design and operation of such a system. The configuration of an injection system is determined by the volume of the sample plug that is to be delivered to the separation process. Accordingly, this paper addresses the design and testing of injection systems with a variety of configurations, including a simple cross, a double-T, and a triple-T configuration. This paper also presents the design of a unique multi-T injection configuration. Each injection system cycles through a predetermined series of steps, in which the electric field magnitude and distribution within the various channels is strictly manipulated, to effectuate a virtual valve. The uniquemulti-T configuration injection system presented within this paper has the ability to simulate the functions of the cross, double-T, and triple-T systems through appropriate manipulations of the electric field within its various channels. In other words, the proposed design successfully combines several conventional injection systems within a single microfluidic chip.
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Abstract
Automation of electrophoretic microchips for sequential analysis of different samples is demonstrated. This system used an autosampler, which was on-line connected to the microchip and the whole process including sample loading and injection, analysis and data acquisition as well as washing were all automated. Rhodamin B at different concentrations was first loaded into a hydrodynamic flow stream by an autosampler, delivered to the microchip, and then sequentially injected into the electrophoretic microchannel for analysis and detection. Automation was achieved by running two independent programs, one for sample loading by an autosampler and the other one for electrophoretic injection by voltage switching, on the same computer. Using this sampling chip, each loaded volume (0.2-1 microL) can be injected for dozens of electrophoretic analyses (1-10 nL for each injection). The variances caused by the external connections, which did not affect the electrophoretic analysis but would cause band broadening of the loaded sample in the hydrodynamic flow stream, were theoretically deduced. Results indicate that the dead volume (approximately 300 nL) due to the connection fitting on the chip could lead to dilution of the loaded sample by a factor of one when 0.2 microL of sample was loaded. Such a design allows sequential analysis of a series of samples while the running buffer is continuously pumped into the connection capillary as well as microchannels for washing between two loaded samples to minimize cross contamination without human intervention. Using this sampling chip, the required sample amount and handling time can be greatly reduced compared to the manual method.
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185
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Chen SH, Lin YH, Wang LY, Lin CC, Lee GB. Flow-through sampling for electrophoresis-based microchips and their applications for protein analysis. Anal Chem 2002; 74:5146-53. [PMID: 12380842 DOI: 10.1021/ac0202886] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
This work presents a model behind the operation of a flow-through sampling chip and its application for immunoseparation, as well as its integration with a wash/elution bed for protein purification, concentration, and detection. This device used hydrodynamic pressure to drive the sample flow, and a gating voltage was applied to the electrophoretic channel on the microchip to control the sample loading for the separation and to inhibit sample leakage. The deduced model indicates that the critical gating voltage (VC) that is defined as the minimum gating voltage applied to the microchip for sampling is a function of the pump flow rate, the configuration of the microchannel on the chip, and the electroosmosis of the buffer solution. It was found that the theoretical V(C) values calculated from the measured electroosmotic mobilities and flow split ratios were comparable to those experimentally obtained from two microchips with different sampling channel sizes. This had an error percentage ranging from 1 to 20%. Because the hydrodynamic flow is insensitive to electrophoretic mobility, this electrophoresis-based microchip device was free of injection bias due to different ionic strength and electrophoretic mobility in the sample. Additionally, the usefulness of this device was demonstrated for the study of affinity interactions. Mixtures of Cy5-labeled bovine serum albumin (Cy5-BSA) and anti-BSA in various proportions were introduced into the microchip via a syringe pump, and the immunocomplex was electrophoretically separated from the free Cy5-BSA on the microchip. Based on the relative intensity of the free and complex BSA, the binding constant of BSA and anti-BSA was estimated as 3.3 x 10(7) M(-1). Furthermore, a C18 microcartridge (20 microL) was connected to the hydrodynamic inlet of the microchip. Using this device, the wash/elution step can be integrated on-line with the electrophoretic separation and detection on the microchip. Results show that the calibration curve of Cy5-BSA obtained from this integrated device has an R2 value greater than 0.99 and a minimum of quantitation at approximately 10 ng. This direct sampling method is another means of subfractionation, resulting in a relatively greater concentration factor than the average concentration of the whole fraction. Moreover, the electrical field-free bed ensures that the protein interaction will not be affected by the electric field during the wash/elution step.
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Abstract
The geometry and the flow field conditions in the separation microchannel of an electrophoresis chip system may have important impact on the system's separation efficiency. Understanding the geometry effect on the flow field physics in the separation microchannel is beneficial to the design or operation of an electrophoresis system. The turns in a microfabricated separation microchannel generally results in degraded separation quality. To avoid this limitation, channels are constructed with different types of turns to determine the optimum design that minimizes turn-induced band broadening. We have designed and tested various geometric bend ratios to greatly reduce this so-called "racetrack" effect. The effects of the separation channel geometry, fluid velocity profile and bend ratio on the band distribution in the detection area are discussed. Results show that the folded square U-shaped channel is better for miniaturization and simplification. The band tilting was corrected and the racetrack effect reduced in the detection area when the bend ratio is 4:1. The detection time obtained from the present numerical solution matches very well with the experimental data.
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187
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Lin YH, Lee GB, Li CW, Huang GR, Chen SH. Flow-through sampling for electrophoresis-based microfluidic chips using hydrodynamic pumping. J Chromatogr A 2001; 937:115-25. [PMID: 11765077 DOI: 10.1016/s0021-9673(01)01326-7] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
This work presents a novel electrophoretic microchip design which is capable of directly coupling with flow-through analyzers for uninterrupted sampling. In this device, a 3 mm wide sampling channel (SC) was etched on quartz substrate to create the sample inlet and outlet and the 75 microm wide electrophoretic channels were also fabricated on the same substrate. Pressure was used to drive the sample flow through the external tube into the SC and the flow was then split into outlet and electrophoretic channels. A gating voltage was applied to the electrophoretic channel to control the sample loading for subsequent separations and inhibit the sample leakage. The minimum gating voltage required to inhibit the sample leakage depended on the solution buffer and increased with the hydrodynamic flow-rate. A fluorescent dye mixture containing Rhodamine B and Cy3 was introduced into the sample stream at either a continuous or discrete mode via an on-line injection valve and then separated and detected on the microchip using laser-induced fluorescence. For both modes, the relative standard deviation of migration time and peak intensity for consecutive injections was determined to be below 0.6 and 8%, respectively. Because the SC was kept floating, the external sampling equipment requires no electric connection. Therefore, such an electrophoresis-based microchip can be directly coupled with any pressure-driven flow analyzers without hardware modifications. To our best knowledge, this is something currently impossible for reported electrophoretic microchip designs.
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188
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Chen SH, Sung WC, Lee GB, Lin ZY, Chen PW, Liao PC. A disposable poly(methylmethacrylate)-based microfluidic module for protein identification by nanoelectrospray ionization-tandem mass spectrometry. Electrophoresis 2001; 22:3972-7. [PMID: 11700728 DOI: 10.1002/1522-2683(200110)22:18<3972::aid-elps3972>3.0.co;2-6] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The design, fabrication, and analytical use of a poly(methylmethacrylate) (PMMA)-based microfluidic module for nanoelectrospray ionization-tandem mass spectrometry (nano-ESI-MS/MS) were described. The microfluidic module can be mass-produced at low costs and used as a disposable device to generate nano-ESI-MS/MS signals for protein identification from low amounts of protein samples. Compared with commercially available nanospray capillary tips, the module gave comparable signal quality and also offered advantages in convenience and easiness of operation, permitting repeated usage, and disposability.
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189
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Sung WC, Lee GB, Tzeng CC, Chen SH. Plastic microchip electrophoresis for genetic screening: The analysis of polymerase chain reactions products of fragile X (CGG)n alleles. Electrophoresis 2001; 22:1188-93. [PMID: 11358146 DOI: 10.1002/1522-2683()22:6<1188::aid-elps1188>3.0.co;2-p] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Clinical screening of abnormal chromosomes associated with fragile X syndrome (FXS) demands a high-throughput method including DNA sizing and detection of the amplified products. This study is to explore the use of polymer microchip electrophoresis for the analysis of polymerase chain reaction (PCR) products of fragile X (CGG)n alleles to facilitate a fast exclusion test of FXS. The sequences flanking the CGG-repeat of FMR1 gene was amplified by betaine-PCR and the amplified products were desalted and then analyzed by microchips which were fabricated on poly(methyl methacrylate) (PMMA) substrate. The PCR bands with more than six CGG-repeats in difference could be clearly distinguished in less than 3 min by microchip electrophoresis with a separation length of 6 cm. It was found that the signal was greatly enhanced with the use of both covalent (Cy5) and intercalating dye (TORRO-3), which has never been demonstrated before. We tested the method by reanalysis of twelve samples from males and six samples from females. For female samples with less than six repeat differences, Southern blotting method was performed to confirm or exclude the findings from microchips. It was found that the test results from all male and female samples show a 100% correlation between the microchip electrophoresis and the existing methods.
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190
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Kim DG, Park SY, You KR, Lee GB, Kim H, Moon WS, Chun YH, Park SH. Establishment and characterization of chromosomal aberrations in human cholangiocarcinoma cell lines by cross-species color banding. Genes Chromosomes Cancer 2001. [PMID: 11107175 DOI: 10.1002/1098-2264(2000)9999:9999<::aid-gcc1053>3.0.co;2-p] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Cholangiocarcinoma (CC), a malignant neoplasm of the biliary epithelium, is usually fatal because of difficulty in early diagnosis and lack of availability of effective therapy. Furthermore, little is known about the genetics and biology of CC. Only a few reports concerning cytogenetic studies of CC have been published, and few cell lines have been established. We recently established four CC cell lines, designated as SCK, JCK, Cho-CK, and Choi-CK, and report the first application of cross-species color banding (RxFISH) and multiple chromosome painting for the characterization of the chromosomal rearrangements of these CC cell lines. Each cell line had unique modal karyotypic characteristics and showed a variable number of numerical and structural clonal cytogenetic aberrations. Chromosomes 3, 6, 7, 8, 12, 14, 17, and 18 were commonly involved in structural abnormalities. Homogeneously staining regions were determined in SCK and JCK, and double minute chromosomes were found in Cho-CK. The chromosomal aberrations of the four CC cell lines were effectively analyzed by RxFISH and FISH with multiple chromosome painting probes. The nonrandom rearrangements suggest candidate regions for isolation of genes related to CC.
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191
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Kim DG, Park SY, You KR, Lee GB, Kim H, Moon WS, Chun YH, Park SH. Establishment and characterization of chromosomal aberrations in human cholangiocarcinoma cell lines by cross-species color banding. Genes Chromosomes Cancer 2001; 30:48-56. [PMID: 11107175 DOI: 10.1002/1098-2264(2000)9999:9999<::aid-gcc1053>3.0.co;2-p] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Cholangiocarcinoma (CC), a malignant neoplasm of the biliary epithelium, is usually fatal because of difficulty in early diagnosis and lack of availability of effective therapy. Furthermore, little is known about the genetics and biology of CC. Only a few reports concerning cytogenetic studies of CC have been published, and few cell lines have been established. We recently established four CC cell lines, designated as SCK, JCK, Cho-CK, and Choi-CK, and report the first application of cross-species color banding (RxFISH) and multiple chromosome painting for the characterization of the chromosomal rearrangements of these CC cell lines. Each cell line had unique modal karyotypic characteristics and showed a variable number of numerical and structural clonal cytogenetic aberrations. Chromosomes 3, 6, 7, 8, 12, 14, 17, and 18 were commonly involved in structural abnormalities. Homogeneously staining regions were determined in SCK and JCK, and double minute chromosomes were found in Cho-CK. The chromosomal aberrations of the four CC cell lines were effectively analyzed by RxFISH and FISH with multiple chromosome painting probes. The nonrandom rearrangements suggest candidate regions for isolation of genes related to CC.
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192
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Lee GB, Ogilvie BM. The intestinal mucus barrier to parasites and bacteria. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1982; 144:247-8. [PMID: 7080918 DOI: 10.1007/978-1-4615-9254-9_38] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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193
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Elder GH, Lee GB, Tovey JA. Decreased activity of hepatic uroporphyrinogen decarboxylase in sporadic porphyria cutanea tarda. N Engl J Med 1978; 299:274-8. [PMID: 661926 DOI: 10.1056/nejm197808102990603] [Citation(s) in RCA: 141] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
To investigate the role of uroporphyrinogen decarboxylase in the pathogenesis of the sporadic form of porphyria cutanea tarda, we measured this enzyme in liver, erythrocytes and cultured skin fibroblasts, and also measured coproporphyrinogen oxidase and the total iron concentration in liver. The mean uroporphyrinogen decarboxylase activity was lower in liver from seven male patients (9.0 pmol of coproporphyrin per minute per milligram of protein) than in 12 controls, including seven with alcoholic liver disease (22.3 pmol per minute per milligram; P less than 0.05). Coproporphyrinogen oxidase activities were the same in each group. Liver iron concentrations were lower during remission, but uroporphyrinogen decarboxylase activities were not related to clinical activity for uroporphyrin excretion. Erythrocyte and fibroblast enzyme activities were the same as in normal subjects. A hepatic uroporphyrinogen decarboxylase defect is a prerequisite for the development of porphyria cutanea tarda, but other factors, which probably do not alter uroporphyrinogen decarboxylase activity, determine the clinical onset. In sporadic porphyria cutaneous tarda, the enzyme defect appears to be restricted to the liver.
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194
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Lewis RA, Lee GB, Martonyi CL, Barnett JM, Falls HF. Familial foveal retinoschisis. ARCHIVES OF OPHTHALMOLOGY (CHICAGO, ILL. : 1960) 1977; 95:1190-6. [PMID: 880078 DOI: 10.1001/archopht.1977.04450070088006] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Three young women, offspring of a nonconsanguineous marriage of normal parents, manifested mild visual loss associated with a bilateral foveal dystrophy that resembled the macular involvement in juvenile sex-linked retinoschisis. Electrophysiologic and psychophysiologic tests showed less severe involvement than the gonosomal equivalent. An autosomal recessive inheritance is proposed.
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195
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Abstract
In a patient who had a family history of ulcerative colitis and colonic carcinoma, a jejunal lymphosarcoma developed four years after resection for Crohn's disease of the small intestine. It is suggested that the association of lymphosarcoma with Crohn's disease is more than a chance association.
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196
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Anderson MT, Lee GB, Campion BC, Amplatz K, Tuna N. Cardiac dysrhythmias associated with exercise stress testing. Am J Cardiol 1972; 30:763-7. [PMID: 4673518 DOI: 10.1016/0002-9149(72)90152-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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197
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Griffith OH, Lesch GH, Rempfer GF, Birrell GB, Burke CA, Schlosser DW, Mallon MH, Lee GB, Stafford RG, Jost PC, Marriott TB. Photoelectron microscopy: a new approach to mapping organic and biological surfaces. Proc Natl Acad Sci U S A 1972; 69:561-5. [PMID: 4501573 PMCID: PMC426507 DOI: 10.1073/pnas.69.3.561] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
A general method of imaging organic and biological surfaces based on the photoelectric effect is reported. For the experiments, a photoelectron emission microscope was constructed. It is an ultrahigh vacuum instrument using electrostatic electron lenses, microchannel plate image intensifier, cold stage, hydrogen excitation source, and magnesium fluoride optics. The organic surfaces examined were grid patterns of acridine orange, fluorescein, and benzo(a)pyrene on a Butvar surface. A biological sample, sectioned rat epididymis, was also imaged by the new photoelectron microscope. Good contrast was obtained in these initial low magnification experiments. These data demonstrate the feasibility of mapping biological surfaces according to differences in ionization potentials of exposed molecules. A number of technical difficulties, such as the intensity of the excitation source, must be solved before high resolution experiments are practical. However, it is probable that this approach can be useful, even at low magnifications, in determination of the properties of organic and biological surfaces.
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198
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Mears TV, Levitan AA, Rietbrock MJ, Hawkinson H, Lee GB. Profound diuresis associated with mitral regurgitation. A case report. MINNESOTA MEDICINE 1971; 54:939-41. [PMID: 5113707] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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199
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Lee GB, Campion BC. Management of dysrhythmias associated with acute myocardial infarction. 2. Postgrad Med 1971; 50:217-23. [PMID: 5130352 DOI: 10.1080/00325481.1971.11697677] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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200
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