Mode of interaction and apparent binding constants of meso-tetraaryl porphyrins bearing between one and four positive charges with DNA

Meso-substituted porphyrins, ((4-N-methyl-pyridyl)n(Ph)4-n)PH2, n = 1 to 4, bearing between 1 and 4 positive charges have been synthetized and studied for their interaction with Calf Thymus DNA. Competition binding experiments using ethidium bromide or one of its dimers show that these porphyrins and some of their Cu(II) or Fe(III)Cl complexes have apparent binding constants between 3 10(5) and 5 10(7) M-1. Fluorescence energy transfer experiments show that not only the tetracationic previously described porphyrin but also the tri- and dicationic porphyrins are able to intercalate into DNA. These data indicate a greater importance of the polyaromatic porphyrin ring than of the number or position of the positive charges for meso-tetra-arylporphyrin interaction with DNA.     

Dicationic pyridium porphyrins appending different peripheral substituents: synthesis and studies for their interactions with DNA

Twelve trans-dicationic pyridium porphyrins appending different peripheral substituents were synthesized and their abilities to bind and cleave DNA under irradiation have been investigated. Their binding modes to DNA were studied by UV-vis spectroscopy, circular dichroism. The apparent constants were measured by EB competitive fluorescence method and most of them were in the range of 10(4)-10(5) M(-1). We found that both the position of positive charges and steric hindrance could greatly influence their binding affinities and modes to DNA, and then affect their photocleaving abilities to DNA.     

Interaction of cationic porphyrins with DNA: importance of the number and position of the charges and minimum structural requirements for intercalation

Thirty-three porphyrins or metalloporphyrins corresponding to the general formula [meso-[N-methyl-4(or 3 or 2)-pyridiniumyl]n(aryl)4-nporphyrin]M (M = H2, CuII, or ClFeIII), with n = 2-4, have been synthesized and characterized by UV-visible and 1H NMR spectroscopy and mass spectrometry. These porphyrins differ not only in the number (2-4) and position of their cationic charges but also in the steric requirements to reach even temporarily a completely planar geometry. In particular, they contain 0, 1, 2, 3, or 4 meso-aryl substituents not able to rotate. Interaction of these porphyrins or metalloporphyrins with calf thymus DNA has been studied and their apparent affinity binding constants have been determined by use of a competition method with ethidium bromide which was applicable not only for all the free base porphyrins but also for their copper(II) or iron(III) complexes. Whatever their mode of binding may be, their apparent affinity binding constants were relatively high (Kapp between 1.2 x 10(7) and 5 x 10(4) M-1 under our conditions), and a linear decrease of log Kapp with the number of porphyrin charges was observed. Studies of porphyrin-DNA interactions by UV and fluorescence spectroscopy, viscosimetry, and fluorescence energy transfer experiments showed that not only the tetracationic meso-tetrakis[N-methyl-4(or 3)-pyridiniumyl]porphyrins, which both involved four freely rotating meso-aryl groups, but also the corresponding tri- and dicationic porphyrins were able to intercalate into calf thymus DNA. Moreover, the cis dicationic meso-bis(N-methyl-2-pyridiniumyl)diphenylporphyrin, which involved only two freely rotating meso-aryl groups in a cis position, was also able to intercalate. The other meso-(N-methyl-2-pyridiniumyl)n(phenyl)4-nporphyrins, which involved either zero, one, or two trans freely rotating meso-aryl groups, could not intercalate into DNA. These results show that only half of the porphyrin ring is necessary for intercalation to occur.     

Syntheses and DNA binding of new cationic porphyrin-tetrapeptide conjugates

Recently cationic porphyrin-peptide conjugates were synthesized to enhance the cellular uptake of porphyrins or deliver the peptide moiety to the close vicinity of nucleic acids. DNA binding of such compounds was not systematically studied yet.We synthesized two new porphyrin-tetrapeptide conjugates which can be considered as a typical monomer unit corresponding to the branches of porphyrin-polymeric branched chain polypeptide conjugates. Tetra-peptides were linked to the tri-cationic meso-tri(4-N-methylpyridyl)-mono-(4-carboxyphenyl)porphyrin and bi-cationic meso-5,10-bis(4-N-methylpyridyl)-15,20-di-(4-carboxyphenyl)porphyrin. DNA binding of porphyrin derivatives, and their peptide conjugates was investigated with comprehensive spectroscopic methods. Titration of porphyrin conjugates with DNA showed changes in Soret bands with bathocromic shifts and hypochromicities. Decomposition of absorption spectra suggested the formation of two populations of bound porphyrins.Evidence provided by the decomposition of absorption spectra, fluorescence decay components, fluorescence energy transfer and induced CD signals reveals that peptide conjugates of di- and tricationic porphyrins bind to DNA by two distinct binding modes which can be identified as intercalation and external binding. Tri-cationic structure and elimination of negative charges in the peptide conjugates are preferable for the binding. Our findings provide essential information for the design of DNA-targeted porphyrin-peptide conjugates.     

Tricationic pyridium porphyrins appending different peripheral substituents: experimental and DFT studies on their interactions with DNA

Four tricationic pyridium porphyrins appending hydroxyphenyl, methoxyphenyl, propionoxyphenyl or carboxyphenyl group at meso-20-position of porphyrin core have been synthesized and their abilities to bind and cleave DNA have been investigated. Using a combination of absorption, fluorescence, circular dichroism (CD) spectra, thermal DNA denaturation as well as viscosity measurements, their binding modes and intrinsic binding constants (K_b) to calf DNA (CT DNA) were comparatively studied and also compared with those of 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP). The results suggest that the K_b values of these porphyrins are greatly influenced by the number of positive charges and steric hindrance. Theoretical calculations applying the density functional theory (DFT) have been carried out and explain their DNA-binding properties reasonably. The efficiency of DNA photocleavage by these porphyrins shows high dependence on the values of K_b.     

Thermodynamic and kinetic analysis of porphyrin binding to Trichosanthes cucumerina seed lectin.

The interaction of several metallo-porphyrins with the galactose-specific lectin from Trichosanthes cucumeirna (TCSL) has been investigated. Difference absorption spectroscopy revealed that significant changes occur in the Soret band region of the porphyrins upon binding to TCSL and these changes have been monitored to obtain association constants (Ka) and stoichiometry of binding (n). The dimeric lectin binds two porphyrin molecules and the presence of the specific saccharide lactose did not affect porphyrin binding significantly, indicating that the sugar and the porphyrin bind at different sites. The Ka values obtained for the binding of different porphyrins with TCSL at 25 degrees C were in the range of 2 x 10(3)-5 x 10(5) m(-1). Association constants for meso-tetra(4-sulphonatophenyl)porphyrinato copper(II) (CuTPPS), a porphyrin bearing four negative charges and meso-tetra(4-methylpyridinium)porphyrinato copper(II) (CuTMPyP), a porphyrin with four positive charges, were determined at several temperatures; from the temperature dependence of the association constants, the thermodynamic parameters change in enthalpy (DeltaH degrees ) and change in entropy (DeltaS degrees ) associated with the binding process were estimated. The thermodynamic data indicate that porphyrin binding to TCSL is driven largely by a favourable entropic contribution; the enthalpic contribution is very small, suggesting that the binding process is governed primarily by hydrophobic forces. Stopped-flow spectroscopic measurements show that binding of CuTMPyP to TCSL takes place by a single-step process and at 20 degrees C, the association and dissociation rate constants were 1.89 x 10(4) m(-1).s(-1) and 0.29 s(-1), respectively.     

86 Characterization and differentiation of binding modes of water-soluble porphyrins at complexation with DNA

The influence of water-soluble cationic meso-tetra-(4?N-oxyethylpyridyl)porphyrin (H₂TOEPyP4) and it’s metallocomplexes with Ni, Cu, Co, and Zn on hydrodynamic and spectral behavior of DNA solutions has been studied by UV/Vis absorption and viscosity measurement. It was shown that the presence of planar porphyrins such as H₂TOEPyP4, NiTOEPyP4, and СuTOEPyP4 leads to an increase in viscosity at relatively small concentrations, and then decrease to stable values. Such behavior is explained by intercalation of these porphyrins in DNA structure because the intercalation mode involves the insertion of a planar molecule between DNA base pairs which results in a decrease in the DNA helical twist and lengthening of the DNA. Further decrease of viscosity is explained by the saturation intercalation sites and occurs outside the binding mode. But, in the case of porphyrins with axial ligands such as CoTOEPyP4 and ZnTOEPyP4, the hydrodynamic parameters decrease, which is explained by self-stacking of these porphyrins in DNA surface. This data are proved by spectral measurements. The results obtained from titration experiments were used for calculation of binding parameters: the binding constant K _b and the number of binding sites per base pair n. Obtained data reveal that K _b varies between 3.4 and 5.4?×?10⁶?M^?1 for a planar porphyrins, a range typical for intercalation mode interactions, and 5.6?×?10⁵?M^?1 and 1.8?×?10⁶?M^?1 for axial porphyrins. In addition, the exclusion parameter n also testifies that at intercalation, (n～2) the adjacent base pairs are removed to place the planar molecules, and for outside binders to pack on the surface needs too few places (n～0.5–1). It is apparent that the binding is somewhat stronger at intercalation. The viscometric and spectrophotometric measurements are in good agreement.     

The importance of coulombic end effects: experimental characterization of the effects of oligonucleotide flanking charges on the strength and salt dependence of oligocation (L8+) binding to single-stranded DNA oligomers.

Binding constants Kobs, expressed per site and evaluated in the limit of zero binding density, are quantified as functions of salt (sodium acetate) concentration for the interactions of the oligopeptide ligand KWK6NH2 (designated L8+, with ZL = 8 charges) with three single-stranded DNA oligomers (ss dT-mers, with |ZD| = 15, 39, and 69 charges). These results provide the first systematic experimental information about the effect of changing |ZD| on the strength and salt dependence of oligocation-oligonucleotide binding interactions. In a comparative study of L8+ binding to poly dT and to a short dT oligomer (|ZD| = 10),. Proc. Natl. Acad. Sci. USA. 93:2511-2516) demonstrated the profound thermodynamic effects of phosphate charges that flank isolated nonspecific L8+ binding sites on DNA. Here we find that both Kobs and the magnitude of its power dependence on salt activity (|SaKobs|) increase monotonically with increasing |ZD|. The dependences of Kobs and SaKobs on |ZD| are interpreted by introducing a simple two-state thermodynamic model for Coulombic end effects, which accounts for our finding that when L8+ binds to sufficiently long dT-mers, both DeltaGobso = -RT ln Kobs and SaKobs approach the values characteristic of binding to poly-dT as linear functions of the reciprocal of the number of potential oligocation binding sites on the DNA lattice. Analysis of our L8+-dT-mer binding data in terms of this model indicates that the axial range of the Coulombic end effect for ss DNA extends over approximately 10 phosphate charges. We conclude that Coulombic interactions cause an oligocation (with ZL < |ZD|) to bind preferentially to interior rather than terminal binding sites on oligoanionic or polyanionic DNA, and we quantify the strong increase of this preference with decreasing salt concentration. Coulombic end effects must be considered when oligonucleotides are used as models for polyanionic DNA in thermodynamic studies of the binding of charged ligands, including proteins.     

A series of meso-tris(N-methyl-pyridiniumyl)-(4-alkylamidophenyl) porphyrins: Synthesis,interaction with DNA and antibacterial activity

A series of meso-5,10,15-tris(N-methyl-4-pyridiniumyl)-20-(4-alkylamidophenyl) porphyrins were synthesized by derivatizing the amino group on the phenyl ring with the following hydrophobic groups: –C(O)C₇F₁₅, –C(O)CHCH₂, C(O)CH₃, –C(O)C₇H₁₅, and –C(O)C₁₅H₃₁. The cationic tris-pyridiumyl porphyrin core serves as a DNA binding motif and a photosensitizer to photomodify DNA molecules. The changes of the UV–Vis absorption spectra during the titration of these porphyrins with calf thymus DNA revealed a large bathochromic shift (up to 14 nm) and a hypochromicity (up to 55%) of the porphyrins Soret bands, usually considered as proof of porphyrin intercalation into DNA. Association constants (K) calculated according to the McGhee and von Hippel model, were in the range of 10⁶–10⁷ M⁻¹. An increase in hydrophobicity of the substituents at the 20−meso-position produced higher binding affinity. These porphyrins caused photomodification of the supercoiled plasmid DNA when a green laser beam at 532 nm was applied. Those with higher surface activity acted more efficiently as DNA photomodifiers. The porphyrin with a perfluorinated alkyl chain (–COC₇F₁₅) at the meso-20-position inhibited the growth of gram-positive bacteria (S. aureus, or S. epidermidis). Other porphyrins exhibited moderate activity against both gram-negative and gram-positive organisms.     

Binding and photocleavage of cationic porphyrin-phenylpiperazine hybrids to DNA

The binding properties of cationic porphyrin-phenylpiperazine hybrids to calf thymus (CT) DNA were investigated by using absorption, fluorescence and circular dichroism (CD) spectra, and the apparent affinity binding constants (K(app)) of the porphyrins for CT DNA were determined by using a competition method with ethidium bromide (EB). Intercalation of porphyrin into CT DNA occurred when two phenylpiperazines were introduced at cis position onto the periphery of cationic porphyrin. The photocleavages of pBR322 plasmid DNA by the porphyrins were consistent with the values of K(app). With [porphyrin]/[DNA base pairs] ratio increased, the binding mode tended to be outside binding, and the cleavage abilities of the porphyrins varied. In the presence of sodium azide, a quencher of 1O2, the cleavage of DNA by the porphyrin of intercalation was less inhibited.     

Optical absorption and fluorescence spectroscopy studies of ground state melanin-cationic porphyrins complexes.

Optical absorption and fluorescence spectroscopies were employed in the study of the interaction between synthetic L-dopa (dihydroxyphenylalanine) melanin and the cationic porphyrins tetrakis(4-N-methylpyridyl) porphyrin (TMPyP), tetrakis(4-N-benzylpyridyl)porphyrin (TBzPyP), zinc tetrakis(4-N-methylpyridyl)porphyrin (ZnTMPyP) and zinc tetrakis (4-N-benzylpyridyl)porphyrin (ZnTBzPyP). Optical absorption and fluorescence properties of the porphyrins were dependent on the symmetry of the central ring. No evidence was found for dimerization of the porphyrins in phosphate buffer, pH 7, in the concentration range between 4 x 10(-8) to 5 x 10(-5) M. Addition of L-dopa melanin red shifted the optical absorption spectra of porphyrins, concomitant to broadening and reduction in intensity of the bands. L-Dopa melanin also strongly quenched the fluorescence of the porphyrins. Time resolution of the fluorescence decay of porphyrins showed at least two lifetimes that were only slightly modified in the presence of melanin. The interaction between melanin and porphyrin resulted in the formation of non-fluorescent ground state complexes. It was found that there are two different classes of binding sites in melanin for complexation with cationic porphyrins and the values of dissociation constants are of the order of 10(-8) M. These values and the number of binding sites are dependent on the nature of the porphyrins. It was shown that the binding has electrostatic origin, but it is also affected by metal coordination and hydrophobic interaction.     

Thermodynamic analysis of porphyrin binding to Momordica charantia (bitter gourd) lectin.

Owing to the use of porphyrins in photodynamic therapy for the treatment of malignant tumors, and the preferential interaction of lectins with tumor cells, studies on lectin-porphyrin interaction are of significant interest. In this study, the interaction of several free-base and metalloporphyrins with Momordica charantia (bitter gourd) lectin (MCL) was investigated by absorption spectroscopy. Difference absorption spectra revealed that significant changes occur in the Soret band region of the porphyrins on binding to MCL. These changes were monitored to obtain association constants (Ka) and stoichiometry of binding. The tetrameric MCL binds four porphyrin molecules, and the stoichiometry was unaffected by the presence of the specific sugar, lactose. In addition, the agglutination activity of MCL was unaffected by the presence of the porphyrins used in this study, clearly indicating that porphyrin and carbohydrate ligands bind at different sites. Both cationic and anionic porphyrins bind to the lectin with comparable affinity (Ka =10(3)-10(5) m(-1)). The thermodynamic parameters associated with the interaction of several porphyrins, obtained from the temperature dependence of the Ka values, were found to be in the range: DeltaH degrees = -98.1 to -54.4 kJ.mol(-1) and DeltaS degrees =-243.9 to -90.8 J.mol(-1).K(-1). These results indicate that porphyrin binding to MCL is governed by enthalpic forces and that the contribution from binding entropy is negative. Enthalpy-entropy compensation was observed in the interaction of different porphyrins with MCL, underscoring the role of water structure in the overall binding process. Analysis of CD spectra of MCL indicates that this protein contains about 13%alpha-helix, 36%beta-sheet, 21%beta-turn, and the rest unordered structures. Binding of porphyrins does not significantly alter the secondary and tertiary structures of MCL.     

Interactions with glutathione S-transferases of porphyrins used in photodynamic therapy and naturally occurring porphyrins.

Several naturally occurring porphyrins and porphyrins used in photodynamic therapy inhibit glutathione S-transferase isoenzymes either purified from rat liver or lung or in cytosol from normal and from cancerous (Morris 7288C hepatoma) liver. Although differences occur in the type and amount of transferases in normal and cancerous liver and in the liver of rats bearing an extrahepatic tumour, these enzymes are potential binding sites for porphyrins. Porphyrin structure is an important factor in determining the affinity of binding, as shown by the relative inhibitory effectiveness. Of the dicarboxylic porphyrins in the mixture used clinically, OO'-diacetylhaematoporphyrin and monohydroxyethylmonovinyldeuteroporphyrin are more effective inhibitors than haematoporphyrin and protoporphyrin IX. Of the naturally occurring porphyrins the order of effectiveness is protoporphyrin IX (dicarboxylic) greater than coproporphyrin (tetracarboxylic) greater than uroporphyrin (octacarboxylic) and type I greater than type III isomers of both uroporphyrin and coproporphyrin, and the synthetic tetra-meso-phenylporphinetetrasulphonate is a better inhibitor (apparent Ki = 250 nM) than coproporphyrin, which contains a comparable number of negative charges. In addition, iron-porphyrin chelates are more effective inhibitors of the transferases, with 25-fold decrease in Ki value, than the free porphyrins. These results indicate that one means whereby porphyrins accumulate in tissues is the occupation of intracellular binding sites, such as the transferases. Since porphyrins inhibit the activity of these important detoxifying enzymes, there will be metabolic consequences to the cell.     

Thermodynamic studies on the interaction of water-soluble porphyrins with the glucose/mannose-specific lectin from garden pea (Pisum sativum)

Due to the application of porphyrins as photosensitizers in photodynamic therapy to treat cancer, and the ability of some lectins to preferentially recognize tumor cells, studies on the interaction of porphyrins with lectins are of considerable interest. Here we report thermodynamic studies on the interaction of several free-base and metallo-porphyrins with pea (Pisum sativum) lectin (PSL). Association constants (Ka) were obtained by absorption titrations by monitoring changes in the Soret band of the porphyrins and the Ka values obtained for various porphyrins at different temperatures are in the range of 1.0 x 10(4) to 8.0 x 10(4) M(-1). Both cationic and anionic porphyrins were found to bind to PSL with comparable affinity. Presence of 0.1 M methyl-alpha-D-mannopyranoside--a carbohydrate ligand that is specifically recognised by PSL--did not affect the binding significantly, suggesting that porphyrin and sugar bind at different sites on the lectin. From the temperature dependence of the Ka values, the thermodynamic parameters, change in enthalpy and change in entropy associated with the binding process were estimated. These values were found to be in the range: delthaH degree = -95.4 to -33.9 kJ x mol(-1) and deltaS degree = -237.2 to -32.2 J x mol(-1) x K(-1), indicating that porphyrin binding to pea lectin is driven largely by enthalpic forces with the entropic contribution being negative. Enthalpy-entropy compensation was observed in the interaction of different porphyrins to PSL, with the exception of meso-tetra-(4-sulfonatophenyl)porphyrinato zinc(II), emphasizing the role of water structure in the overall binding process. Circular dichroism and differential scanning calorimetric studies indicate that while porphyrin binding does not induce significant changes in the lectin structure and thermal stability, carbohydrate binding induces moderate changes in the tertiary structure of the protein and also increases its thermal unfolding temperature and the enthalpy of the unfolding transition.     

Interaction of metallopyrazoliumylporphyrins with calf thymus DNA.

The interaction of transition metal complexes of cationic porphyrins bearing five membered rings, meso-tetrakis(1,2-dimethylpyrazolium-4-yl)porphyrin (MPzP, M=Mn(III), Ni(II), Cu(II) or Zn(II)), with calf thymus DNA (ctDNA) has been studied. Metalloporphyrins NiPzP and CuPzP are intercalated into the 5'GC3' step of ctDNA. MnPzP is bound edge-on at the 5'TA3' step of the minor groove of ctDNA, while ZnPzP is bound face-on at the 5'TA3' step of the major groove of ctDNA. The binding constants of the metalloporphyrins to ctDNA range from 1.05x10(5) to 2.66x10(6) M(-1) and are comparable to those of other reported cationic porphyrins. The binding process of the metallopyrazoliumylporphyrins to ctDNA is endothermic and entropically driven. These results have revealed that the kind of central metal ions of metalloporphyrins influences the binding characteristics of the porphyrin to DNA.     

Interaction of an Fe derivative of TMAP (Fe(TMAP)OAc) with DNA in comparison with free-base TMAP

We investigated the interaction of meso-tetrakis (N-para-methylanilium) porphyrin (TMAP) in its free base and Fe(II) form (Fe(TMAP)OAc) as a new derivative, with high molecular weight DNA at different ionic strengths, using various spectroscopic methods and microcalorimetry. The data obtained by spectrophotometery, circular dichroism (CD), fluorescence quenching and resonance light scattering (RLS) have demonstrated that TMAP association with DNA is via outside binding with self-stacking manner, which is accompanied with the "end-on" type complex formation in low ionic strength. However, in the case of Fe(TMAP)OAc, predominant mode of interaction is groove binding and after increasing in DNA concentration, unstable stacking-type aggregates are formed. In addition, isothermal titration calorimetric measurements have indicated the exothermic process of porphyrins binding to DNA, but the exothermisity in metal derivative of porphyrin is less than the free base. It confirmed the formation of a more organized aggregate of TMAP on DNA surface. Interactions of both porphyrins with DNA show high sensitivity to ionic strength. By addition of salt, the downfield CD signal of TMAP aggregates is shifted to a higher wavelength, which indicates some changes in the aggregates position. In the case of Fe(TMAP)OAc, addition of salt leads to changes in the mode of binding from groove binding to outside binding with self-stacking, which is accompanied with major changes in CD spectra, possibly indicating the formation of "face-on" type complex.     

A supramolecular enzyme model catalyzing the central cleavage of carotenoids

Several bis-beta-cyclodextrin porphyrins have been prepared as supramolecular receptors of carotenoids. The binding constants of carotenoids to receptors were determined by quenching the fluorescence of the porphyrins on hydrophobic binding of carotenoids within the cavities of cyclodextrins. K(a)=8.3 x 10(6) M(-1) was calculated for binding of beta,beta-carotene to bis-beta-cyclodextrin Zn porphyrin. The corresponding Ru complex catalyzes the central cleavage of carotenoids in the presence of tert-butyl hydroperoxide in a biphasic system.     

Molecular orientation of porphyrins accompanying the formation of chain-aligned DNA films

Porphyrin-containing DNA solid films with several binding orientations were successfully prepared by drying the aqueous solution of porphyrins and DNA in a magnetic field. By the measurement of linear dichroism absorption spectra from three identical spatial directions, the molecular orientations of porphyrins in chain-aligned DNA films were evaluated. Tetra(N-methylpyridinium-4-yl)-porphyrin was found to be bound at the surface of DNA chains like a patch. This orientation is different from the intercalative or groove binding manners observed in solutions. In contrast, tetra(4-sulfonatophenyl)-porphyrin exhibited an orientation perpendicular to the DNA axis, which may be attributed to H-aggregation of porphyrins along the direction parallel to DNA chains. Heme-protein with coiled coil backbone was also aligned along the DNA chains, orienting ferric protoporphyrin parallel to the magnetic field. The major effect for these molecular orientations would be the molecular packing of the rod-disk or the rod-rod systems.     

Detection of DNA recognition events using multi-well field effect devices

We proposed the multi-well field effect device for detection of charged biomolecules and demonstrated the detection principle for DNA recognition events using quasi-static capacitance-voltage (QSCV) measurement. The multi-well field effect device is based on the electrostatic interaction between molecular charges induced by DNA recognition and surface electrons in silicon through the Si(3)N(4)/SiO(2) thin double-layer. Since DNA molecules and DNA binders such as Hoechst 33258 have intrinsic charges in aqueous solutions, respectively, the charge density changes due to DNA recognition events at the Si(3)N(4) surface were directly translated into electrical signal such as a flat band voltage change in the QSCV measurement. The average flat band shifts were 20.7 mV for hybridization and -13.5 mV for binding of Hoechst 33258. From the results of flat band voltage shifts due to hybridization and binding of Hoechst 33258, the immobilization density of oligonucleotide probes at the Si(3)N(4) surface was estimated to be 10(8) cm(-2). The platform based on the multi-well field effect device is suitable for a simple and arrayed detection system for DNA recognition events.