Quaternary ammonium functionalized clay film electrodes modified with polyphenol oxidase for the sensitive detection of catechol

Naturally occurring Cameroonian smectite clay has been grafted with trimethylpropylammonium (TMPA) groups and the resulting organoclay has been deposited onto a glassy carbon electrode surface as a suitable immobilization matrix for polyphenol oxidase (PPO). High sensitivity of the electrochemical device to catechol biosensing can be achieved when the enzyme was impregnated within the organoclay film subsequent to its deposition due to favorable electrostatic interaction between PPO and the TMPA-clay layer. The bioelectrode preparation method was also compatible with the use of a mediator (i.e., ferrocene) and the best performance was obtained with a three-layer configuration made of glassy carbon coated with a first layer of ferrocene (Fc), which was then covered with the PPO-impregnated TMPA-clay layer, and finally overcoated with an enzyme-free TMPA-clay film acting as a protecting overlayer to avoid leaching of the biomolecule in solution. The electrochemical behavior of the modified film electrodes was first characterized by cyclic voltammetry and, then, they were evaluated for the amperometric biosensing of the model analyte catechol in batch conditions and in flow injection analysis. Various experimental parameters likely to influence the biosensor response have been investigated, including the electrode preparation mode (composition configuration, thickness), the usefulness of a mediator, the operating potential and pH of the medium, as well as the advantageous features of the TMPA-clay in comparison to related film electrodes based on non-functionalized clays. The organoclay was found to provide a favorable environment to enzyme activity and the multilayer configuration of the film electrode to provide a biosensor with good characteristics, such as an extended linear range for catechol detection (2 x 10(-8) to 1.2 x 10(-5)M) and a detection limit in the nanomolar range (9 x 10(-9)M).     

聚3，4乙烯二氧噻吩修饰的新型碳纳米管纤维电极及其电化学性能评价

目的 植入式脑机接口在神经疾病的治疗方面已经得到了广泛应用，治疗的效果依赖于与神经组织接触的电极。与刚性材料制作的电极相比，碳基微纤维电极尺度小、生物兼容性好、组织炎症反应小，可以减少植入后的异物反应，改善神经记录信号的信噪比，可以长期保持稳定的电极特性。方法 本文设计了一种柔性碳纳米管（carbon nanotubes，CNTs）纤维电极的修饰方法，该方法采用电化学聚合的方式可以将聚3,4-乙烯二氧噻吩（poly（3,4-ethylenedioxythiophene），PEDOT）薄膜沉积到CNTs纤维电极上，作为微电极涂层。为了证明修饰涂层在电极表面具有良好的机械稳定性，对修饰电极进行了超声处理。此外，本文将PEDOT薄膜沉积到ITO玻璃上，评价了PEDOT薄膜的生物相容性。结果 恒电流方式在CNTs纤维电极表面沉积的PEDOT涂层降低了电极的电化学阻抗，提高了电极的电化学性能，且PEDOT沉积的时间越长阻抗减少的幅度越明显。对电极进行超声处理后，电极的电化学阻抗没有产生显著变化，说明超声处理后PEDOT涂层剥离较少，证明了修饰涂层在电极表面具有良好的机械稳定性。最后，细胞实验表明，PEDOT薄膜具有与ITO导电玻璃相当的细胞相容性。结论 PEDOT薄膜可以提高CNTs纤维电极的稳定性，有望提高脑机接口系统的寿命和可靠性，具有应用于长时间记录神经电信号的前景。     

Electrochemical behavior of L-cysteine and its detection at carbon nanotube electrode modified with platinum

The electrochemical behavior of L-cysteine (CySH) on platinum (Pt)/carbon nanotube (CNT) electrode was investigated by cyclic voltammetry. CNTs used in this study were grown directly on graphite disk by chemical vapor deposition. Pt was electrochemically deposited on the activated CNT/graphite electrode by electroreduction of Pt(IV) complex ion on the surface of CNTs. Among graphite, CNT/graphite, and Pt/CNT electrodes, improved electrochemical behavior of CySH oxidation was found with Pt/CNT electrode. On the other hand, a sensitive CySH sensor was developed based on Pt/CNT/graphite electrode. A linear calibration curve can be observed in the range of 0.5 microM-0.1 mM. The detection limit of the Pt/CNT electrode is 0.3 microM (signal/nose=3). Effects of pH, scan rate, and interference of other oxidizable amino acids were also investigated and discussed. Additionally, the reproducibility, stability, and applicability of the Pt/CNT electrode were evaluated.     

Plasma‐Enhanced Atomic Layer Deposition of Ultrathin Oxide Coatings for Stabilized Lithium–Sulfur Batteries

One of the most challenging problems in the development of lithium–sulfur batteries is polysulfide dissolution, which leads to cell overcharge and low columbic efficiency. Here, we propose the formation of a thin conformal Li‐ion permeable oxide layer on the sulfur‐carbon composite electrode surface by rapid plasma enhanced atomic layer deposition (PEALD) in order to prevent this dissolution, while preserving electrical connectivity within the individual electrode particles. PEALD synthesis offers a fast deposition rate combined with a low operating temperature, which allows sulfur evaporation during deposition to be avoided. After PEALD of a thin layer of aluminium oxide on the surface of electrode composed of large (ca. 10 μm in diameter) S‐infiltrated activated carbon fibers (S‐ACF), significantly enhanced cycle life is observed, with a capacity in excess of 600 mA·h·g^?1 after 300 charge–discharge cycles. Scanning electron microscopy (SEM) shows a significant amount of redeposited lithium sulfides on the external surface of regular S‐ACF electrodes. However, the PEALD alumina‐coated electrodes show no lithium sulfide deposits on the fiber surface. Energy dispersive spectroscopy (EDS) studies of the electrodes’ chemical composition further confirms that PEALD alumina coatings dramatically reduce S dissolution from the cathodes by confining the polysulfides inside the alumina barrier.     

Influence of liquid medium and surface morphology on the response of QCM during immobilization and hybridization of short oligonucleotides

With the goal of developing a quartz crystal microbalance (QCM)-based DNA sensor, we have conducted an in situ QCM study along with fluorescence measurements using oligonucleotides (15-mer) as a model single-stranded DNA (ss-DNA) in two different aqueous buffer solutions; the sequence of 15-mer is a part of iduronate-2-sulphate exon whose mutation is known to cause Hunter syndrome, and the 15-mer is thiolated to be immobilized on the Au-coated quartz substrate. The fluorescence data indicate that the initial immobilization as well as the subsequent hybridization with a complementary strand is hardly dependent on the kind of buffer solution. In contrast, the mass increases deducible from the decrease of QCM frequency via the Sauerbrey equation are 2.7-6.2 and 3.0-4.4 times larger than the actual mass increases, as reflected in the fluorescence measurements, for the immobilization and the subsequent hybridization processes, respectively. Such an overestimation is attributed to the trapping of solvent as well as the formation of quite a rigid hydration layer associated with the higher viscosities and/or densities of the buffer solutions. Another noteworthy observation is the excessively large frequency change that occurs when the gold electrode is deposited in advance with Au nanoparticles. This clearly illustrates that the QCM detection of DNA hybridization is also affected greatly by the surface morphology of the electrode. These enlarged signals are altogether presumed to be advantageous when using a QCM system as an in situ probing device in DNA sensors.     

Electrochemical release of ethidium into and fluorescence detection of DNA-ethidium complexes in the diffusion layer at a carbon paste electrode.

The electrochemically controlled release of the ethidium cation from the surface of carbon paste composite electrode was demonstrated using laser-induced fluorescence detection. The electrode contained an ethidium tetracyanoquinodimethane salt. The following experimental parameters were varied in order to optimize the fluorescence intensity: carbon paste composition, electrode potential, voltage pulse time, and laser power. In the presence of calf thymus DNA the fluorescence signal from the diffusion layer was linearly dependent on the logarithm of the DNA concentration over the range from 0.1 to 10(4) ppb.     

Biochemical and immunochemical characterization of the antigen-antibody reaction on a non-toxic biomimetic interface immobilized red blood cells of crucian carp and gold nanoparticles

A special protein assay system based on a highly hydrophilic, non-toxic and conductive biominetic interface has been demonstrated. To fabricate such assay system, red blood cells of crucian carp (RBC) was initially grown on a glassy carbon electrode surface (GCE) deposited nano-sized gold particles (GPs), a second gold nanoparticle layer (NG) was then absorbed on the RBC surface, and finally mammary cancer 15-3 antibody (anti-CA15-3) was attached on the functional RBC surface. A competitive immunoassay format was employed to detect CA15-3 with horseradish peroxidase (HRP)-labeled CA15-3 as tracer and hydrogen peroxide as enzyme substrate. When the immunosensor was incubated into a mixture solution containing HRP-labeled CA15-3 and CA15-3 sample for 1h at 37 degrees C, the amperometric response decreased with the increment of CA15-3 sample concentration. AFM images of the modified layer revealed a uniform distribution of protein and nanogold. In situ QCM and electrochemical measurements demonstrated that the wanted antibody-antigen reactions should occur with high specificity and selectivity. The specific immunoassay system can be developed further to yield sophisticated structures for other proteins.     

A doubly amplified electrochemical immunoassay for carcinoembryonic antigen

An ultrasensitive electrochemical immunoassay (EIA) for the detection of carcinoembryonic antigen (CEA) is described in this report. The assay involves utilizing enzyme-catalyzed deposition of a redox polymer and electrocatalytic oxidation of ascorbic acid (AA) by the deposited redox polymer, a dual-amplification scheme to enhance analytical signals. Briefly, CEA capturing antibody and redox polymer anchoring agent were covalently immobilized on a gold electrode. After incubating with CEA, the electrode was treated in detection antibody-glucose oxidase conjugate solution. Thereafter, it was dipped into the redox polymer solution. Upon the addition of glucose, the redox polymer was enzymatically reduced and deposited on the electrode surface. The deposited redox polymer exhibits excellent electrocatalytic activity towards the oxidation of AA. Consequently, CEA could be quantified amperometrically. This electrochemical immunoassay combines the specificity of the immunological reaction with the sensitivity of the doubly amplified electrochemical detection.     

In-situ FTIR study on adsorption and oxidation of native and thermally denatured calf thymus DNA at glassy carbon electrodes

In-situ Fourier transform infra-red (FTIR) spectra of native and thermally denatured calf thymus DNA (CT DNA) adsorbed and/or oxidized at a glassy carbon (GC) electrode surface are reported. The adsorption of native DNA occurs throughout the potential range (- 0.2 approximately 1.3 V) studied, and the adsorbing state of DNA at electrode surface is changed from through the C=O band of bases and pyrimidine rings to through the C=O of cytosine and imidazole rings while the potential shifts negatively from 1.3 V to -0.2 V. An in-situ FTIR spectrum of native CT DNA adsorbed at GC electrode surface is similar to that of the dissolved DNA, indicating that the structure of CT DNA is not distorted while it is adsorbed at the GC electrode surface. In the potential range of -0.2 approximately1.30 V, the temperature-denatured CT DNA is adsorbed at the electrode surface first, then undergoes electrochemical oxidation reaction and following that, diffuses away from the electrode surface.     

High-sensitive electrochemical detection of point mutation based on polymerization-induced enzymatic amplification

Here a highly sensitive electrochemical method is described for the detection of point mutation in DNA. Polymerization extension reaction is applied to specifically initiate enzymatic electrochemical amplification to improve the sensitivity and enhance the performance of point mutation detection. In this work, 5'-thiolated DNA probe sequences complementary to the wild target DNA are assembled on the gold electrode. In the presence of wild target DNA, the probe is extended by DNA polymerase over the free segment of target as the template. After washing with NaOH solution, the target DNA is removed while the elongated probe sequence remains on the sensing surface. Via hybridizing to the designed biotin-labeled detection probe, the extended sequence is capable of capturing detection probe. After introducing streptavidin-conjugated alkaline phosphatase (SA-ALP), the specific binding between streptavidin and biotin mediates a catalytic reaction of ascorbic acid 2-phosphate (AA-P) substrate to produce a reducing agent ascorbic acid (AA). Then the silver ions in solution are reduced by AA, leading to the deposition of silver metal onto the electrode surface. The amount of deposited silver which is determined by the amount of wild target can be quantified by the linear sweep voltammetry (LSV). The present approach proved to be capable of detecting the wild target DNA down to a detection limit of 1.0×10(-14) M in a wide target concentration range and identifying -28 site (A to G) of the β-thalassemia gene, demonstrating that this scheme offers a highly sensitive and specific approach for point mutation detection.     

Application of electrochemical impedance spectroscopy for monitoring allergen-antibody reactions using gold nanoparticle-based biomolecular immobilization method

Gold nanoparticles were used to enhance the immobilization amount and retain the immunoactivity of recombinant dust mite allergen Der f2 immobilized on a glassy carbon electrode (GCE). The interaction between allergen and antibody was studied by electrochemical impedance spectroscopy (EIS). Self-assembled Au colloid layer (?=16nm) deposited on (3-mercaptopropyl)trimethoxysilane (MPTS)-modified GCE offered a basis to control the immobilization of allergen Der f2. The impedance measurements were based on the charge transfer kinetics of the [Fe(CN)(6)](3-/4-) redox pair, compared with bare GCE, the immobilization of allergen Der f2 and the allergen-antibody interaction that occurred on the electrode surface altered the interfacial electron transfer resistance and thereby slowed down the charge transfer kinetics by reducing the active area of the electrode or by preventing the redox species in electrolyte solution from approaching the electrode. The interactions of allergen with various concentrations of monoclonal antibody were also monitored through the change of impedance response. The results showed that the electron transfer resistance increased with increasing concentrations of monoclonal antibody.     

Interaction of nucleic acids with electrically charged surfaces. VII. The effect of ionic strength of neutral medium on the conformation of dna adsorbed on the mercury electrode

Triangular-wave direct current (d.c.) voltammetry at a hanging mercury drop electrode and phase-selective alternating current (a.c.) polarography at a dropping mercury electrode were used for the investigation of adsorption of double-helical (ds) DNA at mercury electrode surfaces from neutral solutions of 0.05-0.4 M HCOONH4. It was found for the potential region T (from -0.1 V up to ca. -1.0 V) that the height of voltammetric peaks of ds DNA is markedly influenced by the initial potential only at relatively low ionic strength (mu) (from 0.05 up to ca. 0.3). Also a decrease of differential capacity (measured by means of a.c. polarography) in the region T depended markedly on the electrode potential only at relatively low ionic strength. The following conclusions were made concerning the interaction of ds DNA with a mercury electrode charged to potentials of the region T in neutral medium of relatively low ionic strength mu < 0.3). (i) When ds DNA is adsorbed, a significantly higher number of DNA segments is anchored in the positively charged electrode surface than in the surface bearing a negative charge, (ii) In the region T, especially adsorbed labile regions of ds DNA are opened in the electrode surface, which are present in ds DNA already in the bulk of the solution, (iii) In the narrow region of potentials in the Vicinity of the zero charge potential a higher number of ds DNA segments can be opened, probably as a consequence of the strain which could act on the ds DNA molecule in the course of the segmental adsorption/desorption process.     

Adsorption of peptide nucleic acid and DNA decamers at electrically charged surfaces.

Adsorption behavior of peptide nucleic acid (PNA) and DNA decamers (GTAGATCACT and the complementary sequence) on a mercury surface was studied by means of AC impedance measurements at a hanging mercury drop electrode. The nucleic acid was first attached to the electrode by adsorption from a 5-microliter drop of PNA (or DNA) solution, and the electrode with the adsorbed nucleic acid layer was then washed and immersed in the blank background electrolyte where the differential capacity C of the electrode double layer was measured as a function of the applied potential E. It was found that the adsorption behavior of the PNA with an electrically neutral backbone differs greatly from that of the DNA (with a negatively charged backbone), whereas the DNA-PNA hybrid shows intermediate behavior. At higher surface coverage PNA molecules associate at the surface, and the minimum value of C is shifted to negative potentials because of intermolecular interactions of PNA at the surface. Prolonged exposure of PNA to highly negative potentials does not result in PNA desorption, whereas almost all of the DNA is removed from the surface at these potentials. Adsorption of PNA decreases with increasing NaCl concentration in the range from 0 to 50 mM NaCl, in contrast to DNA, the adsorption of which increases under the same conditions.     

Reagentless biosensors based on co-entrapment of a soluble redox polymer and an enzyme within an electrochemically deposited polymer film

A novel biosensor architecture, which is based on the combination of a manual and a non-manual deposition technique for sensor components on the electrode surface is reported. A water-soluble Os-poly(vinyl-imidazole) redox hydrogel is deposited on a graphite electrode by drop-coating (i.e. manually) followed by the electrochemically-induced deposition of an enzyme-containing non-conducting polymer film. The local polymer deposition is initiated by electrochemical generation of H(3)O(+) exclusively at the electrode surface causing a pH-shift to be established in the diffusion zone around the electrode (i.e. non-manually). This pH-shift leads to the protonation of a dissolved polyanionic polymer which in consequence changes significantly its solubility and is hence precipitating on the electrode surface. In the presence of a suitable enzyme, such as quinohemoprotein alcohol dehydrogenase (QH-ADH), the polymer precipitation leads to an entrapment of the redox enzyme within the polymer film. Simultaneously, the water-soluble Os-poly(vinyl-imidazole) redox hydrogel, which is slowly dissolving from the electrode surface after addition of the electrolyte, is co-entrapped within the precipitating polymer layer. This provides the pre-requisite for an efficient electron-transfer pathway from the redox enzyme via the polymer-bound redox centres to the electrode surface. The sensor preparation protocol has been optimised aiming on a high mediator concentration in the polymer film and an effective electron transfer.     

Tribo-electrochemical technique for studying tribocorrosion behavior of biomaterials

Tribocorrosion is the term which describes the synergy between tribological and electrochemical processes. An apparatus was designed and built to study the tribocorrosion behavior of biomaterials. Electrochemical set-up with three electrodes is used for controlling the potential of the surface of a conducting material subjected to classical wear testing. Using this equipment, it is possible to carry out friction and wear tests in electrolytic solution under well-defined electrochemical conditions determined by the applied electrode potential. In this paper, this apparatus was described and the tests of deposited TiN on pure Ti for corrosion and tribocorrosion behavior under simulated body fluid were conducted. The presence of TiN layer on the surface of Ti has increased the open circuit potential. The charge transfer resistance (R(ct)) determined using electrochemical impedance spectroscopy (EIS) was higher for the nitrided surfaces than for the Ti substrates. However after wear test, R(ct) was significantly reduced because the protective layer was damaged.     

Controlling the surface density of DNA on gold by electrically induced desorption

We report on a method to control the packing density of sulfur-bound oligonucleotide layers on metal electrodes by electrical means. In a first step, a dense nucleic acid layer is deposited by self-assembly from solution; in a second step, defined fractions of DNA molecules are released from the surface by applying a series of negative voltage cycles. Systematic investigations of the influence of the applied electrode potentials and oligonucleotide length allow us to identify a sharp desorption onset at -0.65 V versus Ag/AgCl, which is independent of the DNA length. Moreover, our results clearly show the pronounced influence of competitive adsorbents in solution on the desorption behavior, which can prevent the re-adsorption of released DNA molecules, thereby enhancing the desorption efficiency. The method is fully bio-compatible and can be employed to improve the functionality of DNA layers. This is demonstrated in hybridization experiments revealing almost perfect yields for electrically "diluted" DNA layers. The proposed control method is extremely beneficial to the field of DNA-based sensors.     

Three-step electrodeposition synthesis of self-doped polyaniline nanofiber-supported flower-like Au microspheres for high-performance biosensing of DNA hybridization recognition

A three-step electrodeposition method has been successfully adopted to fabricate morphology-controlled novel Au microspheres on self-doped polyaniline nanofibers (nanoSPAN) modified glassy carbon electrode. The deposition conditions, such as HAuCl(4) concentration and deposition step, have significant influences on the morphologies and electrochemical properties of the resulted Au microspheres. Well hierarchical and homogeneously dispersed flower-like Au microspheres (HHFAu) were obtained under optimal conditions by the three-step electrodeposition strategy in 5.0mM HAuCl(4) solution. HHFAu possess large surface area, excellent electron transfer ability and good biocompatibility. The DNA probe could be effectively attached to HHFAu and thus a high-performance DNA biosensor was constructed by using electrochemical impedance spectroscopy as detection method. A gene fragment of the cauliflower mosaic virus 35S gene, which is related to one of the screening genes for the transgenically modified plants, has been satisfactorily detected. The linear range was from 1.0 × 10(-13)M to 1.0 × 10(-6)M and the detection limit was 1.9 × 10(-14)M. This HHFAu/nanoSPAN-based impedance biosensing platform holds great promise for the detection of other biological and chemical molecules.     

Semiquantitative Performance and Mechanism Evaluation of Carbon Nanomaterials as Cathode Coatings for Microbial Fouling Reduction

In this study, we examine bacterial attachment and survival on a titanium (Ti) cathode coated with various carbon nanomaterials (CNM): pristine carbon nanotubes (CNT), oxidized carbon nanotubes (O-CNT), oxidized-annealed carbon nanotubes (OA-CNT), carbon black (CB), and reduced graphene oxide (rGO). The carbon nanomaterials were dispersed in an isopropyl alcohol-Nafion solution and were then used to dip-coat a Ti substrate. Pseudomonas fluorescens was selected as the representative bacterium for environmental biofouling. Experiments in the absence of an electric potential indicate that increased nanoscale surface roughness and decreased hydrophobicity of the CNM coating decreased bacterial adhesion. The loss of bacterial viability on the noncharged CNM coatings ranged from 22% for CB to 67% for OA-CNT and was dependent on the CNM dimensions and surface chemistry. For electrochemical experiments, the total density and percentage of inactivation of the adherent bacteria were analyzed semiquantitatively as functions of electrode potential, current density, and hydrogen peroxide generation. Electrode potential and hydrogen peroxide generation were the dominant factors with regard to short-term (3-h) bacterial attachment and inactivation, respectively. Extended-time electrochemical experiments (12 h) indicated that in all cases, the density of total deposited bacteria increased almost linearly with time and that the rate of bacterial adhesion was decreased 8- to 10-fold when an electric potential was applied. In summary, this study provides a fundamental rationale for the selection of CNM as cathode coatings and electric potential to reduce microbial fouling.     

Carbon fibre-based microbiosensors for in vivo measurements of acetylcholine and choline

This report describes technical improvements to the manufacture of a carbon fibre electrode for the stable and sensitive detection of H2O2 (detection limit at 0.5 microM). This electrode was also modified through the co-immobilisation of acetylcholinesterase (AChE) and/or choline oxidase (ChOx) in a bovine serum albumin (BSA) membrane for the development of a sensor for in vivo measurements of acetylcholine and choline. Amperometric measurements were performed using a conventional three-electrode system forming part of a flow-injection set-up at an applied potential of 800-1100 mV relative to an Ag/AgCl reference electrode. The optimised biosensor obtained was reproducible and stable, and exhibited a detection limit of 1 microM for both acetylcholine and choline. However, due to the high operating potential used, the biosensor was prone to substantial interference from other electroactive compounds, such as ascorbic acid. Therefore, in a further step, a mediated electron transfer approach was used that incorporated horseradish peroxidase into an osmium-based redox hydrogel layered onto the active surface of the electrode. Afterwards, a Nafion layer and a coating containing AChE and/or ChOx co-immobilised in a BSA membrane were successively deposited. This procedure further increased the selectivity of the biosensor, when operated in the same flow-injection system but at an applied potential of -50 mV relative to an Ag/AgCl reference electrode. The sensor exhibited good selectivity and a high sensitivity over a concentration range (0.3-100 microM) suitable for the measurement of choline and acetylcholine in vivo.     

Monte Carlo simulations of supercoiled DNAs confined to a plane.

Recent advances in atomic force microscopy (AFM) have enabled researchers to obtain images of supercoiled DNAs deposited on mica surfaces in buffered aqueous milieux. Confining a supercoiled DNA to a plane greatly restricts its configurational freedom, and could conceivably alter certain structural properties, such as its twist and writhe. A program that was originally written to perform Monte Carlo simulations of supercoiled DNAs in solution was modified to include a surface potential. This potential flattens the DNAs to simulate the effect of deposition on a surface. We have simulated transfers of a 3760-basepair supercoiled DNA from solution to a surface in both 161 and 10 mM ionic strength. In both cases, the geometric and thermodynamic properties of the supercoiled DNAs on the surface differ significantly from the corresponding quantities in solution. At 161 mM ionic strength, the writhe/twist ratio is 1.20-1.33 times larger for DNAs on the surface than for DNAs in solution and significant differences in the radii of gyration are also observed. Simulated surface structures in 161 mM ionic strength closely resemble those observed by AFM. Simulated surface structures in 10 mM ionic strength are similar to a minority of the structures observed by AFM, but differ from the majority of such structures for unknown reasons. In 161 mM ionic strength, the internal energy (excluding the surface potential) decreases substantially as the DNA is confined to the surface. Evidently, supercoiled DNAs in solution are typically deformed farther from the minimum energy configuration than are the corresponding surface-confined DNAs. Nevertheless, the work (Delta A(int)) done on the internal coordinates, which include uniform rotations at constant configuration, during the transfer is positive and 2.6-fold larger than the decrease in internal energy. The corresponding entropy change is negative, and its contribution to Delta A(int) is positive and exceeds the decrease in internal energy by 3.6 fold. The work done on the internal coordinates during the solution-to-surface transfer is directed primarily toward reducing their entropy. Evidently, the number of configurations available to the more deformed solution DNA is vastly greater than for the less deformed surface-confined DNA.