Electrochemical DNA sensing based on gold nanoparticle amplification

A hybridization signal-amplified method based on a gold nanoparticle-supported DNA sequence for electrochemical DNA sensing has been investigated by cyclic voltammetry, differential-pulse voltammetry, and atomic-force microscopy (AFM). Quantitative analysis showed that the peak current increment (Ip) is linearly dependant on the concentration of the gold nanoparticle-supported DNA sequence Au2 over the range 0.51–8.58 pmol L^–1. AFM results indicated that the extent of surface hybridization was dependent on the concentration of the gold-nanoparticle-supported DNA sequence. Moreover, a new pair of peaks, which might arise from the special configuration of the gold-nanoparticle-supported DNA sequence, appeared in the cyclic voltammogram after hybridization. Although quite sensitive, this DNA sensing surface was not easily regenerated, so this kind of amplified method was suitable for disposable DNA sensors and chip-based gene diagnosis sensors.     

Electrochemical sensing of gases based on liquid collection interfaces

Although many electrochemical gas sensors have been reported, electrochemical gas sensors based on liquid collection constitute a smaller subset. Minimally, a liquid interface based electrochemical gas sensor is composed of two electrodes and an ion conducting electrolyte. There is a large number of possible arrangements of these parts, and many choices exist for their composition and preparation methods. This results in a diverse and rich technology now available for gas sensing. The measurement of some analyte gases of interest, notably ozone, nitrogen oxides, hydrogen peroxide, formaldehyde, ammonia, sulfur dioxide and hydrogen sulfide are specifically discussed. Finally, the recent reviews that are likely to be the most relevant to the further development of electrochemical detection approaches for gases with a liquid collection interface are cited and discussed.     

Electrochemical study of thymine dimer based on DNA charge transfer

Differential pulse voltammetry was used to study the formation and level of thymine dimer in DNA duplex modified on a gold electrode. The electrochemical signal of methylene blue coupled with ferricyanide can be obtained via DNA mediated electron transfer, which would be blocked during the formation of thymine dimer. DNA duplexes with different sequences differ in the level of thymine dimer under the same UV irradiation. Futhermore, the presence of guanine base directly preceding -TT- can effectively decrease the level of thymine dimer, possibly due to the self-repair process in which guanine participates. The proposed method can be further applied to DNA self-repair analysis.     

Electrochemical sensing platform based on the carbon nanotubes/redox mediators-biopolymer system

A new electrochemical sensing platform was developed that relied on synergy between carbon nanotubes (CNT) and redox mediators that were co-immobilized in the biopolymer chitosan (CHIT). To demonstrate the concept, the redox mediator Toluidine Blue O (TBO) and CNT were integrated in CHIT and used for the determination of a reduced form of nicotinamide adenine dinucleotide (NADH). As compared to CHIT-TBO, the CHIT-TBO/CNT films displayed large amplification of a current due to the TBO-mediated oxidation of NADH at -0.10 V. This was discussed in terms of the TBO/CNT synergy that resulted in the improved charge propagation through the CHIT-TBO/CNT matrix.     

Electrochemical sensing of target cells based on a peptide/single-strand DNA probe

To electrochemically measure human myeloid leukemia cells (K562 cells), we constructed a probe consisting of peptide/single-strand (ss) DNA. Ac-H₆Y₄C with an acetylated N-terminal of peptide was used to enhance the probe to allow electrode responses that could detect target cells. A ss-DNA was selected as the target cell recognition moiety. The probe exhibits properties that combine the functionalities of both DNA and peptides. The measurement principle is based on changes in the peak currents of the peptide moieties that are caused by interactions between the ss-DNA and target cells. The peak currents were proportional to the concentration of K 562 cells that ranged from 10 to 2,000 cells/mL with a LOD of 3 cells/mL.     

Electrochemical sensing of L-histidine based on structure-switching DNAzymes and gold nanoparticle-graphene nanosheet composites

A sensitive aptasensor for detection of L-histidine based on the switching structure of aptamer and gold nanoparticles-graphene nanosheets (GNPs-GNSs) composite was reported for the first time. The fabricated biosensor shows an expanded linear range, excellent sensitivity and selectivity against other amino acids.     

Fluorescence sensing of anions based on inhibition of excited-state intramolecular proton transfer

Condensation of 2-(2'-aminophenyl)benzoxazole with p-toluenesulfonyl chloride and phenyl isocyanate yields two new anion sensors (TABO and PUBO), which can undergo excited-state intramolecular proton transfer (ESIPT) upon excitation. For the acid receptor TABO, the ESIPT process can be readily disturbed by basic anions such as F-, CH3COO-, and H2PO4- by deprotonating the sulfonamide unit, whereas in the case of PUBO, a good hydrogen-bonding donor, the ESIPT process is inhibited either by the fluoride-induced deprotonation of the urea unit or by the formation of a strong CH3COO--urea intermolecular hydrogen bond complex, and these two types of inhibition mechanisms consequently result in different ratiometric responses. But other anions with less hydrogen-bonding acceptor abilities cannot inhibit the ESIPT. Interestingly, the different inhibition abilities of F-, CH3COO-, and H2PO4- produce different spectral behaviors in PUBO, so this new sensor successfully distinguishes the subtle difference in these three anionic substrates of similar basicity and surface charge density.     

Electrochemical sensing chemical oxygen demand based on the catalytic activity of cobalt oxide film

Cobalt oxide sensing film was in situ prepared on glassy carbon electrode surface via constant potential oxidation. Controlling at 0.8 V in NaOH solution, the high-valence cobalt catalytically oxidized the reduced compounds, decreasing its surface amount and current signal. The current decline was used as the response signal of chemical oxygen demand (COD) because COD represents the summation of reduced compounds in water. The surface morphology and electrocatalytic activity of cobalt oxide were readily tuned by variation of deposition potential, time, medium and Co²⁺ concentration. As confirmed from the atomic force microscopy measurements, the cobalt oxide film, that prepared at 1.3 V for 40 s in pH 4.6 acetate buffer containing 10 mM Co(NO₃)₂, possesses large surface roughness and numerous three-dimensional structures. Electrochemical tests indicated that the prepared cobalt oxide exhibited high electrocatalytic activity to the reduced compounds, accompanied with strong COD signal enhancement. As a result, a novel electrochemical sensor with high sensitivity, rapid response and operational simplicity was developed for COD. The detection limit was as low as 1.1 mg L⁻¹. The analytical application was studied using a large number of lake water samples, and the accuracy was tested by standard method.     

Electrochemical sensing of DNA-adriamycin interactions

Adriamycin, a cancerostatic anthracycline antibiotic, causes considerable death of tumour cells, together with the induction of breaks in DNA single and double strands. The interaction of this compound with DNA was investigated using an electrochemical DNA-biosensor. Adriamycin intercalation in DNA disrupts the double helix and the detection of guanine and 8-oxoguanine could mimic one possible mechanism for the in vivo adriamycin drug action.     

Electrochemical sensing platform based on covalent immobilization of thionine onto gold electrode surface via diazotization-coupling reaction

A novel electrochemical sensing platform by modification of electroactive thionine (Th) onto gold electrode surface was constructed, which was realized by diazotization of 4-aminothiophenol (ATP) self-assembled monolayer, followed by coupling of Th with the diazonium group to form a covalent diazo bond. A pair of well-defined redox peaks of Th was observed in the cyclic voltammetric measurement. The resulting diazo-ATP monolayer displayed superior electrical conductivity, which contributed to the sensitive detection of hydrogen peroxide (H₂O₂). The immobilized Th also showed a remarkable stability, which may benefit from the π-π stacking force and the covalent diazo bond between diazo-ATP and Th molecules. Under the optimized experimental conditions, the current fabricated non-enzyme and reagentless sensor could show a rapid response to H₂O₂ within 3 s and a linear calibration plot ranged from 1.0 × 10⁻⁶ to 6.38 × 10⁻³ M with a detection limit of 6.7 × 10⁻⁷ M. The current fabrication strategy of electroactive interface is expected to be used as a versatile route for the immobilization of more electroactive molecules and offer more opportunities for the applications in electrochemical sensor, biosensor, electrocatalysis, etc.     

Electrochemical examples of multiple-electron transfer

Various electroactive reactants that undergo multipleelectron transfer reactions at electrodes are divided into two broad classes. The first class exhibits a series of single electron steps at different electrode potentials. The second class exhibits multiple-electron transfer in a single voltammetric step. Examples from each class are offered and the reasons for their electrochemical behavior are described.     

Electrochemical non-enzymatic sensing of oxalic acid based on PdPt-modified electrodes: application to the analysis of vegetable samples

Monatshefte für Chemie - Chemical Monthly - The electrocatalytic properties of carbonaceous electrodes, electrochemically modified with microquantities of PdPt (low-platinum-content alloy),...     

基于分子内荧光能量转移的碘聚合膜荧光传感器

合成了基于分子内荧光能量转移的蒽（An）-四苯基卟啉（TPP）双发色团碘荧光探针1．由于An的荧光光谱与TPP的S吸收带具有较好的重叠,供体An与受体TPP之间可以发生有效的分子内荧光能量转移,以An的最大吸收波长作为激发波长时,由于分子内荧光能量转移,受体TPP发出荧光．当碘与探针分子中的识别基团An作用时,导致探针分子的荧光转导基团TPP荧光淬灭．与An、TPP和An＋TPP混合物作敏感材料相比,将探针1固定在PVC膜中制备的敏感膜对碘选择性高、灵敏度好．另外,敏感膜具有很好的重现性、可逆性和稳定性,响应时间小于60S．除Cr2O7^2-和MnO4^-外,食品中常见的无机离子和可能存在的干扰物质不影响碘的测定．在最优条件下,传感器的线性范围为2．04×10^-6-2．36×10^-2mol／L,检出限为3．30×10^-8mol／L．本方法应用于加碘食盐中碘含量的测定,结果满意．     

Colorimetric and ratiometric fluorescence sensing of fluoride ions based on competitive intra- and intermolecular proton transfer

Receptors 1 and 4 show fluoride ion selective changes in their absorbance and emission behaviours amongst F⁻, Cl⁻, Br⁻, I⁻, , CH₃COO⁻, , and anions. Fluoride ion mediated ‘ON-OFF-ON’ switching behaviour of 4 provides opportunities for ratiometric estimation of fluoride ions.     

A fluorescent sensing membrane for iodine based on intramolecular excitation energy transfer of anthryl appended porphyrin

A single anthryl appended meso-tetraphenylporphyrin (TPP) dyad has been synthesized and applied in fluorescence sensing of iodine based on the intramolecular excitation energy transfer. The molecular recognition of the sensor is based on the interaction of iodine with inner anthracene moiety of the dyad, while the signal reporter for the recognition process is the TPP fluorescence quenching. Because the emission spectrum of anthracene is largely overlapped with the Soret band absorption of TPP, intramolecular excitation energy transfer interaction occurs between the donor, anthracene and acceptor, TPP. This energy transfer leads to TPP fluorescence emission by excitation of anthracene. The sensor was constructed by immobilizing the dyad in a plasticized poly(vinyl chloride) (PVC) membrane. The sensing membrane shows higher sensitivity compared to the sensors by using anthracene, TPP, or a mixture of anthracene and TPP as sensing materials. Under the optimum conditions, iodine in a sample solution can be determined from 2.04 to 23.6 mmol·L⁻¹ with a detection limit of 33 nmol·L⁻¹. The sensing membrane shows satisfactory response characteristics including good reproducibility, reversibility and stability, as well as the short response time of less than 60 s. Except for Cr₂O₇²⁻ and MnO₄⁻, other common metal ions and anions in foodstuff do not interfere with iodine determination. The proposed method was applied in the determination of iodine in table salt samples. The results agree well with those obtained by other methods. Supported by the National Outstanding Youth Science Foundation of China (Grant No. 20525518), the National Natural Science Foundation of China (Grant No. 20775005), and the National Natural Science Foundation of Hunan province (Grant No. JJ076021)     

Electrochemical sensing of bisphenol A on single-walled carbon nanotube paper electrodes

The electrochemical detection of BPA often requires modification of electrodes to overcome BPA′s slower kinetics and higher oxidation potential. This work reports a modification-free, paper electrode based on vacuum-filtered SWCNT thin film. The prepared electrode does not need to be polished or transferred into the conducting substrates. The linear sweep voltammetric detection showed a linear response from 0.5–10 μM and 25–100 μM with the experimental LOD of 1.0 μM (S/N=3). The interference study and good recovery percentage (93–105 %) in real water samples demonstrated the method‘s selectivity. The sensor can be promising for developing a simple, low-cost, portable, and paper-based BPA monitoring system.     

Electrochemical impedance sensing of DNA hybridization on conducting polymer film-modified diamond

The impedimetric sensing of DNA hybridization on polyaniline/polyacrylate (PANI/PAA)-modified boron-doped diamond (BDD) electrode has been investigated. An ultrathin film of PANI-PAA copolymer was electropolymerized onto the diamond surfaces to provide carboxylic groups for tethering to DNA sensing probes. The electrochemical impedance and the intrinsic electroactivity of the polymer-diamond interface were analyzed after the hybridization reaction with target and non-target DNA. The impedance measurement shows changes in the impedance modulus as well as electron-transfer resistance at the stage of probe DNA immobilization (single-strand), as well as after hybridization with target DNA (double-strand). DNA hybridization increases the capacitance of the polymer-DNA layer and reduces the overall impedance of the DNA-polymer-diamond stack significantly. The polymer-modified BDD electrode shows no detectable nonspecific adsorption, with good selectivity between the complementary DNA targets and the one-base mismatch targets. The detection limit was measured to be 2 x 10(-8) M at 1000 Hz. Denaturing test on the hybridized probe and subsequent reuse of the probe indicates chemical robustness of the sensor. Our results suggest that electropolymerization followed by the immobilization of biomolecules is a simple and effective way of creating a functional biomolecular scaffold on the diamond surface. In addition, label-free electrochemical impedance method can provide direct and noninvasive sensing of DNA hybridization on BDD.     

Electrochemical sensing of DNA immobilization and hybridization based on carbon nanotubes/nano zinc oxide/chitosan composite film

A novel electrochemical DNA biosensor based on zinc oxide （ZnO） nanoparticles and multi-walled carbon nanotubes （MWNTs） for DNA immobilization and enhanced hybridization detection is presented. The MWNTs/nano ZnO/chitosan composite film modified glassy carbon electrode （MWNTs/ZnO/CHIT/GCE） was fabricated and DNA probes were immobilized on the electrode surface. The hybridization events were monitored by differential pulse voltammetry （DPV） using methylene blue （MB） as an indicator. The sensor can effectively discriminate different DNA sequences related to PAT gene in the transgenic corn, with a detection limit of 2.8× 10^-12 mol/L of target sequence.     

Electrochemical biosensors based on horseradish peroxidase

The principles used for the development of electrochemical biosensors based on horseradish peroxidase are described. Peroxidase is the enzyme which catalyses the oxidation of a variety of organic molecules in the presence of hydrogen peroxide. The features of this enzyme are high catalytic activity and low specificity towards second substrate as well. Horseradish peroxidase may be used as a component of active part of biosensors for the detection of hydrogen peroxide and other compounds when peroxidase is co-immobilized together with other oxidases. Also horseradish peroxidase may be used as a component of detecting system for the biosensors based on biological recognition using specific antibodies, receptors, nucleic acids. The examples of the bio-, immuno-, DNA-sensors developed for the determination of various biologically active compounds are given.