University of North Florida
Browse the Citations
-OR-

Contact Info

Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

View Stuart Chalk's profile on LinkedIn

Dimitrios P. Nikolelis

Abbrev:
Nikolelis, D.P.
Other Names:
Address:
Laboratory of Analytical Chemistry, Department of Chemistry, University of Athens, Panepistimiopolis-Kouponia, GR-15771 Athens, Greece
Phone:
+30-210-7274577
Fax:
+30-210-7274750

Citations 7

"Flow Injection Analysis Of Mixtures Of Dopamine, Adrenaline And Ephedrine In Human Biofluids Using Stabilized After Storage In Air Lipid Membranes With A Novel Incorporated Resorcin[4]arene Receptor"
Electroanalysis 2005 Volume 17, Issue 10 Pages 887-894
Dimitrios P. Nikolelis*, Christina G. Siontorou, George Theoharis, István Bitter

Abstract: This work describes a technique for the rapid, selective and sensitive electrochemical flow injection analysis of mixtures of the stimulating compounds adrenaline, dopamine, and ephedrine using stabilized after storage in air bilayer lipid membranes (BLMs) with incorporated resorcin[4]arene receptor. Injections of the stimulating compounds were made into flowing streams of a carrier electrolyte solution and a transient current signal, with duration of seconds, reproducibly appeared in less than two min after exposure of the lipid membranes to the compounds. The magnitude of this signal was linearly related to the concentration of the compound, which could be determined at micromolar levels. Repetitive cycles of injection of stimulating compounds have shown no signal degradation during each cycle (30 sequential injections). The time of appearance of the transient response was different for each stimulating compound and increased in the order of adrenaline, dopamine and ephedrine. The difference in time of response has allowed selective detection and analysis of these compounds in mixtures. The investigation of the effect of potent interferences included a wide range of compounds usually found in human biofluids, as well as proteins and lipids. The results showed that only proteins (most common in lipid film based biosensors) pose a problem that can be eliminated by modulation of the carrier solution to flow rates that do not allow adsorption of these compounds in the lipid films. The technique was applied in human urine samples.

"Flow Injection Monitoring Of Aflatoxin M-1 In Cheese Using Filter-supported Bilayer Lipid Membranes With Incorporated DNA"
Electroanalysis 2000 Volume 12, Issue 10 Pages 747-751
Christina G. Siontorou, Vangelis G. Andreou, Dimitrios P. Nikolelis, Ulrich J. Krull

Abstract: This work describes a technique for the rapid and sensitive electrochemical flow injection monitoring of aflatoxin M-1 (AFM(1)) in cheese samples. Stabilized filter-supported bilayer lipid membranes (BLMs) were used as detectors Single stranded DNA oligomers terminated with alkyl chains (dT(20)-C-16) were incorporated into the membranes to control surface electrostatic properties. The incorporation of dT(20)-C-16 in BLMs lowered the detection limit for the detection of this toxin by one to four orders of magnitude as compared with the detection limit obtained in the absence of DNA. Therefore, it is now possible to continuously monitor this toxin at concentrations that approached those that could be of interest as set by the U.S. Food and Drug Administration and most European countries. The work described herein takes a significant step towards development of a detector of greater practical potential by demonstrating that the incorporation of C-16-ssDNA into lipid membranes results in a combination of properties that provides for a much more sensitive and robust detection system. Injections of AFM(1) were made into flowing streams of a 0.1 M KCI electrolyte solution, and a transient current signal with duration of seconds reproducibly appeared in about 12 s after exposure of the detector element to the toxin. The magnitude of this signal was linearly related to the concentration of AFM(1) with detection limits at subnanomolar level. The effect of interferents such as proteins and lipids was investigated. It was determined that interferences from proteins could be eliminated by adjustment of the flow rate of the carrier electrolyte solution. The technique was applied for the rapid flow injection determination of aflatoxin MI in cheese samples. AFM(1) could be determined in continuous flowing systems with a rate of at least 3 samples min-1. Repetitive cycles of injection of AFM(1) have shown no signal degradation during each cycle for experiments that attempted over 30 cycles of detection.
Bilayer lipid membranes Extraction

"Flow Injection Monitoring And Analysis Of Mixtures Of Simazine, Atrazine And Propazine Using Filter-supported Bilayer Lipid Membranes"
Electroanalysis 1996 Volume 8, Issue 10 Pages 907-912
Dimitrios P. Nikolelis*, Christina C. Siontorou

Abstract: A microporous glass fiber disk (0.9 cm diameter) was mounted between two plastic layers having a central hole of 0.32 mm diameter. The whole was clamped between two Plexiglass chambers. One of the chambers contained a flow-through electrochemical cell, through which the carrier solution was pumped. A Ag/AgCl reference electrode was immersed in the waste of the carrier solution. The second chamber was equipped with a second Ag/AgCl reference electrode and a potential of 25 mV was applied between the two electrodes. Formation of stabilized BLM was effected by the method of Nikolelis et al. (Ibid.,1995, 7, 531 and Anal. Chem., 1995, 67 936), using solutions of lyophilized egg phosphatidylcholine and dipalmitoylphosphatidic aci d in hexane/ethanol (4:1). The carrier electrolyte solution consisted of 0.1 M KCl/10 mM HEPES buffer of pH 8 containing 1 mM calcium ions. The herbicide solutions were injected into the carrier stream and the resulting transient current signal was recorded. Calibration graphs were linear up to 1.4 ppm, 210 ppb and 300 ppb, respectively, for atrazine, simazine and propazine and the corresponding detection limits were 40, 8 and 20 ppb.
Atrazine Propazine Simazine Amperometry Electrode Buffer

"Bilayer Lipid Membranes As Electrochemical Detectors For Flow Injection Immunoanalysis"
Electroanalysis 1995 Volume 7, Issue 11 Pages 1082-1089
Dimitrios P. Nikolelis, Christina G. Siontorou, Vangelis G. Andreou, Kyriakos G. Viras, Ulrich J. Krull

Abstract: This work describes the use of filter-supported stabilized bilayer lipid membranes (BLMs) for the rapid electrochemical monitoring of an immunological reaction in flowing solution streams. BLMs were prepared from egg phosphatidylcholine (egg PC) and dipalmitoyl phosphatidic acid (DPPA) and the ultrafiltration membranes used were composed of glass microfibers. Thyroxin (T4)/anti-rabbit T4 was used as a representative immunological reaction for these studies. Antibody was incorporated into a floating lipid matrix at an air-electrolyte interface, and then a casting procedure was used to deliver the lipid onto the filter supports for BLM formation. Injections of antigen were made into flowing streams of a carrier electrolyte solution. Experiments were done in a stopped-flow mode using lipid mixtures containing 15% (w/w) DPPA to provide only a single transient current signal with a magnitude related to the antigen concentration. Differential scanning calorimetric experiments provided evidence that the antibody-lipid interactions at the BLMs occurred through electrostatic interactions. BLMs containing 35% DPPA were used to examine regeneration of the active sites of antibody after complex formation by washing with the carrier electrolyte solution. Repetitive cycles of injection of antigen followed by regeneration of antibody binding activity have shown that the maximum number of cycles is about 5, followed by a degradation of signal for a larger number of injections. However, the sensor can also be easily regenerated by recasting of the existing lipid/antibody film at the air-electrolyte interface to form fresh BLMs.

"Selective Continuous Monitoring And Analysis Of Mixtures Of Acesulfame-K, Cyclamate, And Saccharin In Artificial Sweetener Tablets, Diet Soft Drinks, Yogurts, And Wines Using Filter-supported Bilayer Lipid Membranes"
Anal. Chem. 2001 Volume 73, Issue 24 Pages 5945-5952
Dimitrios P. Nikolelis and Spyros Pantoulias

Abstract: This work describes a technique for the rapid and sensitive electrochemical flow injection monitoring and analysis of mixtures of the artificial sweeteners acesulfame-K, cyclamate, and saccharin using stabilized systems of filter-supported bilayer lipid membranes (BLMs). Injections of artificial sweeteners were made into flowing streams of a carrier electrolyte solution, and a transient current signal with duration of seconds reproducibly appeared in less than < 1 min after exposure of the lipid membranes to the artificial sweeteners. The magnitude of this signal was linearly related to the concentration of artificial sweeteners, which could be determined at micromolar levels. Repetitive cycles of injection of artificial sweeteners have shown no signal degradation during each cycle (30 sequential injections). The time of appearance of the transient response was different for each artificial sweetener and increased in the order of cyclamic acid, acesulfame-K, and saccharin. The difference in time of response has allowed selective detection and analysis of these artificial sweeteners in mixtures. The effect of potent interferences, including a wide range of compounds usually found in foods, proteins, and lipids was investigated. The results showed no interferences from these constituents of real food samples. The major interference from proteins (most common in lipid-film-based biosensors) can be eliminated by modulation of the carrier solution that does not allow adsorption of these compounds in BLMs. The technique was applied in real food samples, that is, in artificial sweetener tablets, diet soft drinks, wines, and yogurts that contain mixtures of these artificial sweeteners with aspartame and other compounds. A comparison of results using the present method and that of an Official Method of Analysis showed good agreement between the two methods. [Journal Article; In English; United States]

"Flow Injection Monitoring And Analysis Of Mixtures Of Hydrazine Compounds Using Filter-supported Bilayer Lipid Membranes With Incorporated DNA"
Anal. Chem. 2000 Volume 72, Issue 1 Pages 180-186
Christina G. Siontorou, Dimitrios P. Nikolelis, and Ulrich J. Krull

Abstract: This work describes a technique for the rapid and sensitive electrochemical flow injection monitoring and analysis of mixtures of hydrazine compounds using stabilized systems of filter-supported bilayer lipid membranes (BLMs) composed of egg phosphatidylcholine (egg PC) with incorporated DNA. Injections of hydrazines were made into flowing streams of a carrier electrolyte solution, and a transient current signal with a duration of seconds reproducibly appeared in less than one min after exposure of the DNA-modified lipid membranes to the hydrazines. The magnitude of this signal was linearly related to the concentration of hydrazines, which could be determined at sub-micromolar levels. Repetitive cycles of injection of hydrazines have shown no signal degradation during each cycle (30 sequential injections), The time of appearance of the transient response was different for each hydrazine and increased in the order of hydrazine, methylhydrazine or dimethylhydrazine, and phenylhydrazine. The difference in time of response has snowed selective detection and analysis of these hydrazines in mixtures.

"Bilayer Lipid Membranes For Flow Injection Monitoring Of Acetylcholine, Urea And Penicillin"
Anal. Chem. 1995 Volume 67, Issue 5 Pages 936-944
Dimitrios P. Nikolelis and Christina G. Siontorou

Abstract: Biosensors were fabricated from filter-supported solventless bilayer lipid membranes (BLM) and used for the determination of substrates of hydrolytic enzymes in a flow-through system. The co-deposition of lipid (dipalmitoylphosphatidic acid) and protein solutions to form a BLM on a microporous glass fiber or polycarbonate ultrafiltration membrane disc is described. Enzymes were immobilized on the membranes by incorporating the protein solution into the lipid matrix at the air-electrolyte interface before BLM formation. BLM containing acetylcholinesterase, urease and penicillinase were used for the determination of acetylcholine, urea and penicillin, respectively, following injection of the substrates into a 0.1 M KCl/10 mM HEPES carrier electrolyte. The enzymatic reaction at the membrane surface caused changes in the electrostatic fields and phase structure of the BLM, resulting in ion current transients; the magnitude of these were linearly related to the substrate concentration down to the µM level. The RSD were ~5%. The effects of pH, amount of enzyme and flow rate are discussed. The response times were ~10 s, the detection limits were 1, 10 and 100 µM for acetylcholine, urea and penicillin, respectively, and the analytical throughput was 220 samples/h. This work describes a technique for the rapid and sensitive determination of acetylcholine, urea, and penicillin in flowing solution streams using stabilized systems of solventless bilayer lipid membranes (BLMs). This method of monitoring substrates of hydrolytic enzyme reactions made use of BLMs which were supported on ultrafiltration membranes such as polycarbonate and glass microfiber; these filter membranes were found to enhance the stability of BLMs for uses in flow injection experiments. The enzymes were immobilized on BLMs by incorporating the protein solution into the lipid matrix at the air/electrolyte interface before the BLM formation, followed by injections of the substrates into flowing streams of a carrier electrolyte solution. Hydronium ions produced by the enzymatic reaction at the BLM surface caused dynamic alterations of the electrostatic fields and phase structure of BLMs, and as a result ion current transients were obtained; the magnitude of these signals was correlated to the substrate concentration, which could be determined at the micromolar level. The response times were ~10 s, and acetylcholine, urea, and penicillin could be determined in continuous flowing systems with a maximum rate of 220 samples/h. It is expected that this analytical utility of stabilized BLMs for flow stream uses will provide new opportunities in this strategy of chemical sensing.
Acetylcholine Penicillins Urea Sensor Immobilized enzyme Bilayer lipid membranes