150 New Perspectives in Biosensors Technology and Applications. facilitated the study of biological systems which can be utilized in biosensor devices. catalytic activities and molecular recognition Thus the challenge for synthetic chemistry in. the area of molecular electronics is to prepare molecules with specific and well defined. functions i e that can be used at a molecular level as wires switches diodes etc The. controlled assemblies of supramolecular species selected components allow the preparation. of nanosize materials with quite sophisticated electronic properties De La Rica e Matsui. 1 1 Peptide based nanostructures, The formation of tubular peptide nanostructures has been performed using several different. peptide sequences such as heptapeptide CH3CO Lys Leu Val Phe Phe Ala Glu NH2 Lu. Jacob et al 2003 and dipeptides NH3 Phg Phg COO Reches e Gazit 2004 and NH3 Phe. Trp COO Reches e Gazit 2003 The first peptide nanotubes were obtained by M R. Ghadiri and co workers from cyclic compounds Ghadiri Granja et al 1993 The L amino. acids are the most used building blocks However D amino acids can also self assemble to. form nanofibers similar to those obtained from L amino acids Poteau e Trinquier 2005. The properties of peptides can be modified through changes in the sequence of amino acid. residues used in their preparation providing a highly relevant factor in building these new. systems Poteau e Trinquier 2005 Such changes were reported in a study by varying the D. amino acids D Alanine D Leucine and D phenylanine to obtain different peptide. nanotubes De Santis Morosetti et al 2007 It was observed that by employing enantiomers. D L the possibility of obtaining different supramolecular systems arises with possible. changes in their structural and electronic properties De Santis Morosetti et al 2007. One of the most commonly used peptides in synthesis of nanotubes is NH3 Phe Phe COO. These nanotubes exhibit several unique properties such as high uniformity along the entire. length of the tube biocompatibility stability against various solvents and thermal stability. In this sense there are several studies that investigate the structural control of the nanotubes. by changing variables such as temperature solvent and pH Adler Abramovich Reches et. al 2006 The NH3 Phe Phe COO nanotubes maintain their morphology up to 200 C and. 2010 The thermal stability has been attributed to stacking interactions among aromatic. total degradation or loss of tubular morphology occurs between 200 and 300 C Ryu e Park. residues that mediate the formation of structures Reches e Gazit 2003 The investigation of. stability in different organic solvents shows that the nanotubes do not suffer morphological. changes after treatment in ethanol methanol 2 propanol acetone and acetonitrile Adler. Abramovich Reches et al 2006, Moreover in addition to conformational changes and the sequences of amino acids used in. peptide synthesis of nanomaterials cyclical or linear the amount of amino acids used and. the functional group of the side chains can influence the formation and possibly the desired. application Brea Castedo et al 2007 In this case all the proposed changes and the. preparation methods are in early stages of study and require further research to better. understand their formation and their influence on structural and electronic properties. Yanlian Ulung et al 2009,2 Preparation methods of peptide nanostructures. 2 1 Obtaining nanostructures in liquid phase, The liquid phase method for obtaining nanostructures is divided in two steps To obtain a. nanostructure based on NH3 Phe Phe COO for example the first step is the dissolution. www intechopen com,Biosensors Based on Biological Nanostructures 151. of the compound in an organic solvent 1 1 1 3 3 3 hexafluoro 2 propanol HFP at a. concentration of 100mg mL 1 In the second step nanostructures are obtained in a. spontaneous process after the dilution in water to achieve 2mg mL 1 of concentration By. this protocol NH3 Phe Phe COO self assemble as nanotubes of 80 to 300 nm thick. understood However the most acceptable explanation suggests that the stacking. The self assembling mechanism in which nanotubes are produced is not yet fully. interactions and hydrogen bonds between aromatic rings are responsible for the material. nano organization Reches e Gazit 2003, Another strategy to obtain these materials in liquid phase was proposed by Kim et al Kim. Han et al 2010 In this work the authors used only pure water as solvent and submitted. the system to heating and sonication to dissolve the peptide since NH3 Phe Phe COO. present hydrophobic characteristics and do not dissolve easily in water Nanostructures are. formed after cooling pH values of the preparing media The concentration of the dipeptide. solution was susceptible to variation by the authors in order to comprehend their role in. nanostructure formation Their results showed formation of NH3 Phe Phe COO nanowires. in alkaline media while nanotubes were formed in acidic media Also at high. concentrations of peptide the predominant nanostructures formed are nanowires while at. low concentrations nanotubes are prevalent, 2 2 Nanostructure preparation in solid vapor phase. Peptide nanostructures have been prepared by self assembly oriented in the solid vapor. phase method which consists of using two solvents one to solubilize the peptide and. another one to encourage the nanostructure assemble Based on the bottom up strategy the. first step consists on the formation of a peptide film onto substrate surface usually silicon. with posterior evaporation of the solvent in the absence of humidity In this case the. peptide film is referred to as the solid phase The next step consists of keeping the solid film. in a vapor solvent atmosphere the commonly called vapor phase Parameters like. temperature vapor pressure concentration of solid film and exposure time of the film to. vapor solvent govern the nanostructure formation, Ryu et al described this methodology as the one to obtain 1D nanostructures Ryu e Park. 2008b a The authors studied the influence of temperature and water activity of a solution. containing metallic salts in the nanostructures formation and they reported that. nanostructures are formed at high water activity while for activity values lower than 0 3 no. nanostructures were obtained Also it was observed that nanostructures were only achieved. at a working temperature of 100 to 150 C Fig 1 shows the experimental schematic process. to prepare nanowires or nanotubes in solid vapor phase. The role of the solvent in this process was adapted by Demirel at al Demirel Malvadkar et. al 2010 with a few adaptations During this study the concentration of the precursor. solution was controlled at 2mg mL 1 and the solvent needed at the second step of the solid. vapor process was changed Results show that the nanostructure morphology is related to. the dielectric constant values of the solvents For example results showed that when formed. on water which presents a dielectric constant of 80 1 a tubular structure is obtained Same. structure are obtained when using methanol dielectric constant of 32 6 or ethanol 24 3 as. solvents while solvents presenting dielectric constants much smaller such as toluene 2 4. chloroform 4 8 or tetrahydrofuran 7 5 do not permit the peptide self assembling and no. structure is obtained Scanning electronic micrographs SEM of the nanostructure obtained. at various solvents are shown in Fig 2,www intechopen com. 152 New Perspectives in Biosensors Technology and Applications. Fig 1 Experimental scheme of obtaining peptide nanostructure using solid vapor process. Reprinted with permission from Ryu J and C B Park 2010 High Stability of Self. Assembled Peptide Nanowires Against Thermal Chemical and Proteolytic Attacks. Biotechnology and Bioengineering 105 2 221 230 2010 Wiley Ltd. Fig 2 SEM images of NH3 Phe Phe COO tubes and vesicles a 2mg mL dipeptide in. ethanol vaporized at 25 C b 2mg mL dipeptide in acetone vaporized at 25 C c 2mg mL. dipeptide in ethanol vaporized at 80 C and d 2mg mL dipeptide in acetone vaporized at. 80 C Reprinted with permission from Demirel G N Malvadkar et al 2010 Control of. Protein Adsorption onto Core Shell Tubular and Vesicular Structures of Diphenylalanine. Parylene Langmuir 26 3 1460 1463 2010 American Chemical Society Ltd. www intechopen com,Biosensors Based on Biological Nanostructures 153. 2 3 Obtaining nanostructures for physical vapor deposition. Recently NH3 Phe Phe COO nanotubes were obtained vertically oriented employing the. physical vapor deposition technique Fig 3 Adler Abramovich Aronov et al 2009 Size. and quantity of peptide nanotubes were controlled through deposition parameters. adjustment such as time solvent of preparation temperature and distance between. substrates The peptide nanotubes formation using this technique became possible because. of the low molecular weight and high volatility of precursor species In a typical synthesis. the NH3 Phe Phe COO is heated at 220 C in a vacuum chamber containing a clean. substrate heated at 80 C that is located at the top of the chamber The nanotubes formed. exhibit length of hundreds of micrometers and diameters of 50 to 300nm with morphologies. similar to those from the liquid phase This method has been employed in the fabrication of. electronic devices such as capacitors but it can be used in the modification of electrodes for. electrochemical uses, Fig 3 Proposed assembly mechanism for the formation of vertically aligned ADNTs. a Schematic of the vapor deposition technique During evaporation the NH3 Phe Phe COO. peptide which is heated to 220 C attained a cyclic structure Cyclo NH3 Phe Phe COO. and then assembled on a substrate to form ordered vertically aligned nanotubes b Illustration. of a single peptide nanotube composed mainly of peptide Cyclo NH3 Phe Phe COO. c Molecular arrangement of six Cyclo NH3 Phe Phe COO peptides after energy. minimization A stacking interaction between aromatic moieties of the peptides is suggested. to provide the energetic contribution as well as order and directionality for the initial. interaction Reprinted with permission from Shklovsky J P Beker et al 2010 Bioinspired. peptide nanotubes Deposition technology and physical properties Materials Science and. Engineering B Advanced Functional Solid State Materials 169 1 3 62 66 2009 Elsevier B V. In a recently work this technique was used together with photolithography to enable. peptide nanotubes to assume specific positions in a silicon wafer Shklovsky Beker et al. 2010 The authors used a photoresist wafer with square shaped cavities The schematic. process for the cavities preparation is in Fig 4 According to SEM images presented in Fig 4. dipeptide nanotubes are located over the silicon wafer which is useful to construct. integrated circuits since the orientation and control of nanotubes material size is needed in. such systems,www intechopen com, 154 New Perspectives in Biosensors Technology and Applications. Fig 4 Left Schematic diagram of the peptide nanotubes bundles fabrication process. Right SEM images of patterned arrays of peptide nanotubes fabricated by PVD a Cross. section view of patterned substrate covered by peptide nanotube coating b Top view of. patterned substrate covered by peptide nanotube coating c Top view of peptide nanotube. bundles after HF release d Enlargement view of image c Reprinted with permission from. Shklovsky J P Beker et al 2010 Bioinspired peptide nanotubes Deposition technology. and physical properties Materials Science and Engineering B Advanced Functional Solid. State Materials 169 1 3 62 66 2009 Elsevier B V,2 4 Electrospinning. The electrospinning technique is a technology that uses a high tension electric field 5 50kV. and low currents 0 5 1 A to obtain 1D nanostructures In this process a fluid material is. accelerated and drawn trough an electric field producing structures with reduced diameters. In the work of Singh et al Singh Bittner et al 2008 NH3 Phe Phe COO nanotubes were. prepared from solution in HFP Then this solution was diluted in water to 2 9 mmol L 1 of. concentration and sonicated for 1 hour Variations in the obtaining parameters of the. nanostructures like electric field concentration and flow injection speed on silicon wafer. were investigated and their influence on the nanostructure formation was reported. 3 Functionalization of peptide nanostructures for biosensor applications. In order to obtain some new properties and increase the applicability of peptide. nanomaterials some chemical modification can be performed and materials can be. functionalized to give rise to hybrid compounds Materials that can be employed on. functionalization are nanoparticles polymers and fluorophores among others. Recently Banerjee et al reported the synthesis of peptide nanotubes containing. bis N amido glycylglycine 1 7 heptane dicarboxylate and its modification with. 2 mercaptoethylamine so as to enable its interaction with a Au substrate through a covalent. bond Banerjee Yu et al 2004 In this work the nanomaterial was deposited on a Gold. Au substrate modified with a thiol self assembled monolayer SAM containing cavities. that could be identified by atomic force microscopy AFM AFM images showed that the. modification of the substrate by microfabrication techniques became viable due to the. www intechopen com,Biosensors Based on Biological Nanostructures 155. presence of thiol groups on the outer walls of the nanotubes which can be covalent attached. to the Au substrate allowing the modification of electrodes in specific positions. The gold nanoparticles GNPs were used to ensure thermal and chemical stability and. enzymatic degradation Guha e Banerjee 2009 In this work Ala L Xaa Xaa Val Ile. Phe 1 2 and 3 respectively dipeptides were used and studies confirmed that such sequences. showed thermal stability up to about 80 C and in a wide range of pH 2 10 Guha and. Banerjee have proposed the synthesis of GNPs stabilized by a peptide compound Their. analysis by X ray diffraction indicated that the nanoparticles formed exhibit a diameter of. approximately 7 nm The influence of pH and peptide sequence used in the synthesis of the. GNP coated peptide nanotubes was also studied demonstrating that there is a relationship. between pH and GNP coating that leads to a complete and uniform coverage in one specific. system while in other systems the coverage is partial and shapeless In addition other. parameters were also varied such as the mass ratio between the GNPs and the peptide. nanotube in order to study these interactions pH and GNP coating Fig 5 shows. transmission electronic microscopy TEM images obtained for the peptide nanotubes. functionalized with gold nanoparticles, Fig 5 a c TEM images of dipeptide capped gold nanoparticles fabricated on the outer. surfaces of the dipeptide nanotube 1 3 respectively at pH 10 It is clear from the figure that. at higher pH coating of dipeptide capped GNPs on the outer surfaces of the dipeptide. nanotube is more uniform than at lower pH Reprinted with permission from Guha S and. A Banerjee 2009 Self Assembled Robust Dipeptide Nanotubes and Fabrication of. Dipeptide Capped Gold Nanoparticles on the Surface of these Nanotubes Advanced. Functional Materials 19 12 1949 1961 2009 WILEY VCH Verlag GmbH Co KGaA. In a recent work Martins et al 2011 in press the effect of controlling pH of nanotube. preparation and the concentration of a doping fluorescent molecule on the final structure is. carefully studied Their results showed that structures can vary between nanotubes and. nanoribbons depending on pH of formation and their growth is influenced by the charge. concentration over the nanotubes Fig 6 shows SEM and fluorescence microscopy images. for nanostructures formed at distinct pH ranges, Reches and Gazit studied the formation of peptide nanotubes in a solution containing Fe3O4. magnetite nanoparticles in order to verify the functionalization of peptide nanotubes with. magnetic nanoparticles Reches e Gazit 2006 By SEM images the presence of nanoparticles. www intechopen com, 156 New Perspectives in Biosensors Technology and Applications. onto a surface of peptide nanotube is easily detected These results suggested that these. hybrid systems may find application in sensors and nano electro mechanics devices. Fig 6 a SEM images for nanotubes formed at the concentration of 0 002 m m of pyrenyl. moieties b EPM images 200 times increased for samples of 0 07 m m of pyrenyl. moieties All images for samples produced at distinct pH values. Functionalized peptide nanostructures based on platinum nanoparticles PtNPs were. studied by Song et al Song Challa et al 2004 In this work nanotubes prepared by self. assembly of NH3 D Phe D Phe COO in solution of distinct concentrations were then. functionalized with PtNPs and scanning electron microscopy and Monte Carlo simulations. were used to investigate them Such analyses showed morphological changes related to. concentration At low concentrations nanotubes were obtained whereas at high. concentrations nanovesicles were the products Functionalization was accomplished by. adding K2PtCl4 and ascorbic acid to the solution of peptide nanomaterials The formation of. nanoparticles was verified by the change of solution color Morphological characterization. of nanomaterials functionalized with PtNPs was performed by TEM These materials can. find application in catalysis among others, Peptide nanotubes can also be used as support for the growth of semiconductor. nanocrystals on the nanotubes surface Banerjee Muniz et al 2007 According to the. authors it was possible to grow TiO2 Ge and Cu2S nanocrystals using this technique It was. also found that a simple change in pH causes significant differences in crystal size without. changing their crystallographic properties, The peptide nanomaterials can also encapsulate quantum dots QDs as reported by Yan. and coworkers in which a NH3 Phe Phe COO hydrogel is treated as three dimensional. and interconnected nano scaled fibers that are used in the encapsulation of QDs Yan Cui. et al 2008 Results indicate the promising employment of such materials in nano and. biotechnology,www intechopen com,Biosensors Based on Biological Nanostructures 157. Fig 7 a SEM and b STEM images of PNW PANI core shell nano wires Arrows. indicate the PNW core solid arrows and PANI shell dotted arrows The core shell. structure of the PNW PANI nanowires was clearly visible in STEM micrographs taken in a. bright field imaging mode left and in a high angle angular dark field imaging mode. right Reprinted with permission from Ryu J and C B Park 2009 Synthesis of. Diphenylalanine Polyaniline Core Shell Conducting Nanowires by Peptide Self. Assembly Angewandte Chemie International Edition 48 26 4820 4823 2009 Wiley VCH. Verlag GmbH Co KGaA Weinheim,www intechopen com, 158 New Perspectives in Biosensors Technology and Applications. The obtaining of core shell structures between peptide nanowires PNWs and polyaniline. PANI was also reported Ryu e Park 2009 Vertically oriented nanowires were formed by. using the solid vapor method The nanowires were submitted to chemical modification. using a polymerizing solution of ammonium persulfate APS containing aniline and HCl. 1M to generate the PANI shell along the sidewall of the PNWs The SEM and scanning. transmission electron microscopy STEM images in Fig 7 show the presence of PANI on. the nanowires PNWs core was removed with 1 1 1 3 3 3 hexafluoride 2 propanol HFIP. This material cam be applied as a biosensor in the detection of volatile organic compounds. glucose and hydrogen peroxide,4 Peptide nanomaterials in biosensors. Since the Clark electrode Clark Wolf et al 1953 a remarkable progress has been made on. the development of biosensors for clinical analyses Yoo e Lee 2010 A biosensor is an. integrated receptor transducer device which is capable of providing selective quantitative. or semi quantitative analytical information using a biological recognition element. Thevenot Toth et al 1999 This chapter will emphasize the use of peptide nanomaterials. on development of electrochemical optical and piezoelectric biosensors. 4 1 Electrochemical biosensors, Electrochemical biosensors are currently among the most popular of several types of. biosensors Particularly carbon nanotubes CNTs are excellent materials for the. development of biosensors Wang e Lin 2008 since they exhibit properties which improve. the electron transfer reaction and increase the electrochemical reactivity of enzymatic. products However CNTs are often produced using expensive techniques such as chemical. vapor deposition CVD Such instruments usually need large scale consumption and higher. production costs Recently the use of peptides has attracted the attention of material science. researchers This is attributed to the biocompatibility and molecular recognition of peptides. with other bio molecules or cells resulting in many novel polymer peptide hybrid. molecules as surface modifiers for implants or tissue engineering applications De La Rica e. Matsui 2010, Electrochemical methods of analysis were first applied to peptide nanotubes by Yemini et al. In 2005 Cyclic voltammetry measurements revealed the presence of well defined reversible. anodic and cathodic peaks indicated improved electrochemical reactivity for the potassium. hexacyanoferrate with NH3 Phe Phe COO nanotube modified electrode The effect of the. nanotube deposition on the electrochemical process has also been investigated using. chronoamperometric measurements by application of a potential of 200mV vs Ag AgCl. under continuous stirring of the solution and successive additions of K4Fe CN 6 In this case. the modified electrode has shown significant higher signal about 2 5 fold increase as. compared to the nonmodified electrode The increase of current can be attributed to the high. electroactive surface area The authors also explored the detection potential of peptide. nanotube modified electrodes for measuring hydrogen peroxide in phosphate buffer. solution using peroxidase and 4 acetaminophenol as mediators by applying a potential of. 50 mV The variation of the cathodic current corresponds to quinine NAPQI reduction. allowing indirect detection of hydrogen peroxide in solution Sima Cristea et al 2008 The. current obtained by the modified NH3 Phe Phe COO nanotubes electrode was four times. www intechopen com,Biosensors Based on Biological Nanostructures 159. higher than that obtained for the non modified electrode which is related to the increase of. the functional electrode as previously suggested for CNT which was evidenced by. degradation of the nanostructures by proteinase K on the electrode surface. detection of nicotinamide adenine dinucleotide NADH hydrogen peroxide and. These nanotubes were further used in the construction of amperometric sensors for. ethanol in the absence of redox mediator Yemini Reches Gazit et al 2005 In this case. the NH3 Phe Phe COO nanotubes were used to modify a gold disk electrode surface by. the self assembly process by using Traut s reagent 2 iminothiolane hydrochloride The. cyclic voltammetry of modified electrode in solution containing NADH has shown a. significant increase in the sensitivity of the electrode Fig 8 The peptide nanotube. modified electrode responded significantly and rapidly to the changes in NADH. concentration as observed by amperometric measurement at 0 4 V producing steady. state signals within less than 5 s, Fig 8 Direct measurement of NADH on the peptide nanotube based electrode Left Cyclic. voltammetry of A peptide nanotube based electrode B unmodified electrode measured. in a solution containing 50 mM NADH Scan rate 50 mV s Right Amperometric response. to successive additions of 50 M NADH at 0 4 V vs SCE A Peptide nanotube based. electrode B bare electrode Arrows indicate the addition of increasing concentrations of. NADH Reprinted with permission from Yemini M M Reches et al 2005 Peptide. nanotube modified electrodes for enzyme biosensor applications Analytical Chemistry. 77 16 5155 5159 2005 American Chemistry Society, In developing a biosensor for glucose Yemini and co workers promoted the modification of. the peptide nanotube based gold electrode with glucose oxidase in presence of. glutaraldehyde and PEI polyethyleneimine The detection mechanism is based on the. determination of glucose by monitoring the hydrogen peroxide which is produced by an. enzymatic reaction between glucose oxidase covalently linked to peptide nanotubes by. glutaraldehyde on the gold electrode surface Yemini Reches Gazit et al 2005 Among the. applications this biosensor can be used to detect glucose in urine and blood for the. diagnosis of diabetes and also to monitor the amount of glucose during fermentation. processes in food industry Wang 2008,www intechopen com. 160 New Perspectives in Biosensors Technology and Applications. Fig 9 Various nanoassemblies deposited on a screen printed electrode a b NH3 Nal Nal. COO nanotubes deposited on an electrode illustration and SEM image respectively. c d NH3 Phe Phe COO peptide nanoforest deposited on an electrode illustration and. SEM image respectively e f Boc Phe Phe OH peptide nanospheres deposited on an. electrode illustration and SEM image respectively g Amperometric response of. untreated NH3 Phe Phe COO nanotubes NH3 Nal Nal COO nanotubes and Boc Phe. Phe OH peptide nanospheres on screen printed modi ed electrodes to different phenol. concentrations in 0 1M phosphate buffer 0 1M KCl pH 7 4 Measurements were performed. at 100mV working potential versus Ag AgC Adler Abramovich Badihi Mossberg et al. 2010 Reprinted with permission from Adler Abramovich L M Badihi Mossberg et al. 2010 Characterization of Peptide Nanostructure Modified Electrodes and Their. Application for Ultrasensitive Environmental Monitoring Small 6 7 825 831 2010 Wiley. VCH Verlag GmbH Co KGaA Weinheim,www intechopen com. Biosensors Based on Biological Nanostructures 161, Recently Adler Abramovich and co workers have studied the electrochemical. characterization of NH3 Phe Phe COO nanotubes modified graphite electrodes and. compared them to the CNT based sensor After that the enzyme tyrosinase was. immobilized on these nanostructure modified electrodes for phenol detection Various. methodologies for the pattern deposition of aromatic dipeptide nanotubes and their. horizontal and vertical alignment were also tested Adler Abramovich Badihi Mossberg et. al 2010 For such experiment the authors used NH3 Phe Phe COO nanotubes. naphthylalanil naphthylalanine NH3 Nal Nal COO nanotubes NH3 Phe Phe COO. nanoforests and tert butoxicarbonil Phe Phe OH Boc Phe Phe OH nanospheres Fig 9 In. this case the tubular nanostructures have similar sensitivities while the nanospheres show. sensitivity 14 times higher compared to the untreated electrode The electrodes modified. with nanoforests showed sensitivity 17 times greater than the untreated electrode Fig 8. These results have been explained by the augment of the active area of the electrodes which. was confirmed by Randles Sevcik equation The area calculated for the bare electrode was. 0 02 cm2 After coating it with either NH3 Phe Phe COO or NH3 Nal Nal COO. nanotubes the surface area of the electrode was similar 0 05 cm2 Peptide nanosphere. modification increased the surface area to 0 06 cm2 The highest surface area 0 07 cm2 was. obtained on the electrode coated with the nanoforest Thus the presence of the NH3 Phe. Phe COO nanoforests significantly improves the sensitivity of the biosensor by increasing. the surface area of the electrode and inducing electron transfer in the chemical reaction. Fig 10 SEM images showing stability of the diphenylalanine peptide nanotubes prepared in. pH 7 solution containing microperoxidase 11 intercalated among the different hexagonal. layers of such nanotubes Reprinted with permission from Cipriano T C P M Takahashi. et al 2010 Spatial organization of peptide nanotubes for electrochemical devices Journal. of Materials Science 45 18 5101 5108 Springer Science Business Media LLC 2010. A novel biosensor for hydrogen peroxide was recently developed by combining the known. properties of microperoxidase 11 MP11 as an oxidation catalyst and the interesting. properties of NH3 Phe Phe COO nanotubes PNTs as a supporting matrix Fig 10 in. order to allow a good bioelectrochemical interface Cipriano Takahashi et al 2010 In this. case the synthesized MP11 PNTs were immobilized onto the ITO electrode surface via. www intechopen com, 162 New Perspectives in Biosensors Technology and Applications. Layer by Layer LBL deposition using poly allylamine hydrochloride PAH as positively. charged polyelectrolyte layers The PNTs provided a favorable microenvironment for MP11. to perform direct electron transfer to the electrode surface The resulting electrodes showed. a pair of well defined redox peaks with formal potential at about 343 mV versus SCE in. phosphate buffer solution pH 7 The experimental results also demonstrated that the. resulting biosensor exhibited good electrocatalytic activity to the reduction of H2O2 with a. sensitivity of 9 43 A cm 2 mmol 1 L and a detection limit of 6 mol L 1 at the signal to noise. ratio of 3 These values are expressive when compared with other procedures that involve. immobilization of MP11 onto electrode surfaces that have already been reported in literature. Cipriano Takahashi et al 2010 These values demonstrate that the PNTs can provide a. bridge of electron transfer between protein and electrode The high value obtained for the. detection limit of such analyte can be related to the isolating characteristic of this material. due to wide semiconductor like band gaps when compared to other semiconductor like. organic molecules Moreover we also observed that the peptides self assembly can be. influenced during the change of the pH of the solution The study proved that the. combination of PNTs with MP11 is able to open new opportunities for the design of. enzymatic biosensors with potential applications in practice. Yang and co workers have proposed a novel approach using ionic complementary peptides. EAK16 II to modify a highly ordered pyrolytic graphite electrode and enhance its. compatibility with enzymes for biosensor applications The GOx was covalently. immobilized on the peptide nanofiber matrix through amide bond formation between the. amine groups on GOx and the carboxylate groups of glutamic acid residues on the peptide. Its catalytic activity for glucose oxidation is measured using ferrocenecarboxylic acid FCA. as a mediator for electron transduction The sensitivity was found to be 26 nA mmol 1L mm. 2 which is more than 6 times higher than that obtained with GOx on thiol modified gold. nanotubes and gold electrodes 4 nA mmol 1L mm 2 Yang Fung et al 2009 More. recently metalized peptide nanowires have been employed as conduits for electronic. signals between a redox enzyme NADH peroxidase and a carbon nanotube electrode to. enhance detection sensitivity Yeh Lazareck et al 2007. Another application of peptide nanotubes involves the fabrication of electrochemical. immunosensors In this case the cyclic peptide cyclo Gln D Leu 4 was used for the. formation of nanotubes which was later immobilized onto a substrate of carbon paste Cho. Choi et al 2008 After that the immobilization of antibody anti E coli O157 H7 was carried. out onto the surface of the tubes This immobilization is possible due to the bond formed. between the carboxylic group present in the surface of the nanotubes and the amine groups. present in the enzyme structure This immobilization was confirmed by fluorescence. microscopy images showing the functionalization of the surface with the antibody The. antigen antibody interaction onto the surface of the electrode modified with nanotubes was. confirmed by SEM Fig 11 and electrochemical studies indicating potential applications in. the development of electrochemical immunosensors for detection of pathologies such as E. De la Rica and co workers reported a significant improvement in the electrochemical. behavior of pathogen sensors using peptide nanotubes for sensor chip fabrication In this. work bola amphiphilic peptide monomers self assembly to form peptide nanotubes and. then they were coated by antibodies in a simple incubation process De La Rica Mendoza et. al 2008 Pathogen detection is achieved due to the difference in the dielectric properties of. viral particles and water molecules Hence binding viruses to the peptide nanotubes. www intechopen com,Biosensors Based on Biological Nanostructures 163. decreases the permittivity of the medium surrounding the nanotube and consequently. decreases the capacitance between electrodes In this device configuration the major role of. the nanotubes is to concentrate targeted viruses selectively by molecular recognition at this. location At this position impedimetric detection with the electrodes is most sensitive De. La Rica Mendoza et al 2008, Fig 11 SEM Image of attaching E coli O157 H7 cells on the surface of peptide nanotubes by. antigen antibody interaction Reprinted with permission from Cho E C J W Choi et al. 2008 Fabrication of an electrochemical immunosensor with self assembled peptide. nanotubes Colloids and Surfaces a Physicochemical and Engineering Aspects 313 95 99. 2007 Elsevier B V, In another approach membranes for dynamic sensors of ions were obtain throught the self. assembled nanotubes vertically aligned under the substrate Motesharei et al verified that. peptide nanotubes provide channels for ion selection due to their hydrophobic character. and the possibility of orientation during immobilization on the gold substrate through thiol. monolayers Motesharei Ghadiri 1997 These channels were obtained from peptide. nanotubes synthesized using D Leu and L Trp aminoacids Hartgerink Granja et al 1996. The immobilization of nanotubes onto gold substrate was oriented by thiol monolayers in. two methodologies The first methodology consisted of immersing gold substrate in an. ethanolic solution containing either 1 dodecanethiol or dodecyl sulfide for 12 hours After. the formation of the monolayer the electrode was washed with ethanol dried in N2 gas and. immersed in an ethanolic solution 0 1 mmol L 1 of cyclic peptide for 12 hours In the second. methodology the gold substrate was immersed in an ethanolic solution composed of 10. mmol L 1 of 1 dodecanethiol or dodecyl sulfide and cyclic peptide 0 1 mmol L 1 during 12. hours After the formation of the monolayer the electrode was washed using ethanol and. dried in Ar, The orientation of self assembled cyclic peptides was verified by grazing angle FTIR. spectroscopy through the band absorption of amide group compared to the band related to. the N H stretching Such comparison is justified based on the attenuation of the stretching. N H bond caused by the presence of gold onto the horizontally oriented nanotube. FTIR analysis showed that both substrates modified by methodology 1 using thiol and. thioether presented greater amount of peptide tubular structures perpendicular to substrate. due high intensity in peak at 1635 cm 1 attributed to amine groups The lower intense peaks.
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