Ferrocene Signal Research Articles

A Novel CRISPR/Cas12a-Mediated Ratiometric Dual-Signal Electrochemical Biosensor for Ultrasensitive and Reliable Detection of Circulating Tumor Deoxyribonucleic Acid.

Circulating tumor DNA (ctDNA) holds great promise as a noninvasive biomarker for cancer diagnosis, treatment, and prognosis. However, the accurate and specific quantification of low-abundance ctDNA in serum remains a significant challenge. This study introduced, for the first time, a novel exponential amplification reaction (EXPAR)-assisted CRISPR/Cas12a-mediated ratiometric dual-signal electrochemical biosensor for ultrasensitive and reliable detection of ctDNA. To implement the dual-signal strategy, a signal unit (ssDNA-MB@Fc/UiO-66-NH2) was prepared, consisting of methylene blue-modified ssDNA as the biogate to encapsulate ferrocene signal molecules within UiO-66-NH2 nanocarriers. The presence of target ctDNA KRAS triggered EXPAR amplification, generating numerous activators for Cas12a activation, resulting in the cleavage of ssDNA-P fully complementary to the ssDNA-MB biogate. Due to the inability to form a rigid structure dsDNA (ssDNA-MB/ssDNA-P), the separation of ssDNA-MB biogate from the UiO-66-NH2 surface was hindered by electrostatic interactions. Consequently, the supernatant collected after centrifugation exhibited either no or only a weak presence of Fc and MB signal molecules. Conversely, in the absence of the target ctDNA, the ssDNA-MB biogate was open, leading to the leakage of Fc signal molecules. This clever ratiometric strategy with Cas12a as the "connector", reflecting the concentration of ctDNA KRAS based on the ratio of the current intensities of the two electroactive signal molecules, enhanced detection sensitivity by at least 60-300 times compared to single-signal strategies. Moreover, this strategy demonstrated satisfactory performance in ctDNA detection in complex human serum, highlighting its potential for cancer diagnosis.

A CRISPR-Cas12a-based electrochemical biosensor for the detection of microphthalmia-associated transcription factor.

Anovel electrochemical biosensor that combines the CRISPR-Cas12a system with a gold electrode is reportedfor the rapid and sensitive detection of microphthalmia-associated transcription factor (MITF). The biosensor consists of a gold electrode modified with DNA1, which contains the target sequence of MITF and is labeled with ferrocene, an electroactive molecule. The biosensor also includes hairpin DNA, which has a binding site for MITF and can hybridize with helper DNA to form a double-stranded complex that activates CRISPR-Cas12a. When MITF is present, it binds to hairpin DNA and prevents its hybridization with helper DNA, thus inhibiting CRISPR-Cas12a activity and preserving the DPV signal of ferrocene. When MITF is absent, hairpin DNA hybridizes with helper DNA and activates CRISPR-Cas12a, which cleaves DNA1 and releases ferrocene, thus reducing the DPV signal. The biosensor can detect MITF with high sensitivity (with an LOD of 8.14 fM), specificity, and accuracy in various samples, such as cell nuclear extracts and human serum. The biosensor can also diagnose and monitor melanocyte-related diseases and melanin production. This work provides a simple, fast, sensitive, and cost-effective biosensor for MITF detection and a valuable tool for applications in genetic testing, disease diagnosis, and drug screening.

Dually Amplified Electrochemical Aptasensor for Endotoxin Detection via Target-Assisted Electrochemically Mediated ATRP.

As the entering of bacterial endotoxin into blood can cause various life-threatening pathological conditions, the screening and detection of low-abundance endotoxin are of great importance to human health. Taking advantage of signal amplification by target-assisted electrochemically mediated atom transfer radical polymerization (teATRP), we illustrate herein a simple and cost-effective electrochemical aptasensor capable of detecting endotoxin with high sensitivity and selectivity. Specifically, the aptamer receptor was employed for the selective capture of endotoxin, of which the glycan chain was then decorated with ATRP initiators via covalent coupling between the diol sites and phenylboronic acid (PBA) group, followed by the recruitment of ferrocene signal reporters via the grafting of polymer chains through potentiostatic eATRP under ambient temperature. As the glycan chain of endotoxin can be decorated with hundreds of ATRP initiators while the further grafting of polymer chains through eATRP can recruit hundreds to thousands of signal reporters to each initiator-decorated site, the teATRP-based strategy allows for the dual amplification of the detection signal. This dually amplified electrochemical aptasensor has the ability to sensitively and selectively detect endotoxin at a concentration as low as 1.2 fg/mL, and its practical applicability has been further demonstrated using human serum samples. Owing to the simplicity, high efficiency, biocompatibility, and inexpensiveness of the teATRP-based amplification strategy, this electrochemical aptasensor holds great application potential in the sensitive and selective detection of low-abundance endotoxin and many other glycan chain-containing bio-targets.

Target-Synergized Biologically Mediated RAFT Polymerization for Electrochemical Aptasensing of Femtomolar Thrombin.

The assay of thrombin levels is integral to the assessment of coagulation function and clinical screening of coagulation disorder-related diseases. In this work, we illustrate the ingenious use of the target-synergized biologically mediated reversible addition-fragmentation chain transfer (RAFT) polymerization (tsBMRP) as a novel amplification strategy for the electrochemical aptamer-based biosensing of thrombin at the femtomolar levels. Briefly, the tsBMRP-based strategy relies on the boronate affinity-mediated decoration of the glycan chain(s) of the target itself with RAFT agents and the subsequent recruitment of signal labels via BMRP, mediated by the direct reduction of RAFT agents by NADH into initiating/propagating radicals. Obviously, the tsBMRP-based strategy is biologically friendly, low-cost, and simple in operation. As thrombin is a glycoconjugate, its electrochemical aptasensing involves the use of the thrombin-binding aptamer (TBA) as the recognition receptor, the site-specific decoration of RAFT agents to the glycan chain of thrombin via boronate affinity, and further the recruitment of ferrocene signal labels via the BMRP of ferrocenylmethyl methacrylate (FcMMA). As boronate affinity results in the decoration of each glycan chain with tens of RAFT agents while BMRP recruits hundreds of signal labels to each RAFT agent-decorated site, the tsBMRP-based strategy allows us to detect thrombin at a concentration of 35.3 fM. This electrochemical aptasensor is highly selective, and its applicability to thrombin detection in serum samples has been further demonstrated. The merits of high sensitivity and selectivity, low cost, good anti-interference capability, and simple operation make the tsBMRP-based electrochemical thrombin aptasensor great promise in biomedical and clinical applications.

An ultrasensitive and specific ratiometric electrochemical biosensor based on SRCA-CRISPR/Cas12a system for detection of Salmonella in food

Sensitive and specific detection of Salmonella is highly desirable to guarantee food safety and prevent food-borne disease outbreaks. Herein, we proposed a ratiometric electrochemical biosensor based on the combination of SRCA and CRISPR/Cas12a system for ultrasensitive and specific detection of Salmonella. Signal amplification is accomplished by reasonably integrating rapid SRCA amplification and the trans-cleavage capabilities of Cas12a. Accordingly, the non-specific amplification was eliminated. Compared with single signal-based electrochemical approaches, the ratiometric electrochemical measurements offer self-calibration to reduce the internal/external disturbances, thereby achieving precise analytical performance and high reliability. At this strategy, based on the ratio of the current signal of ferrocene (Fc) and methylene blue (MB) (IFc/IMB), the biosensor displayed a linear range from 5.8 fg/μL to 5.8 ng/μL and detected as low as 2.08 fg/μL of Salmonella in pure cultures. For the detection of the actual samples, this biosensor was 100% sensitivity, 97.8% specificity and 98% accuracy in comparison with the international standard. And the detection results of this biosensor were consistent with real-time fluorescent quantitative PCR (RT-qPCR), which further verified the accuracy and practical application value of the biosensor. Overall, this strategy provides a valuable platform for highly specific and ultrasensitive screening of Salmonella in food.

A signal on-off ratiometric electrochemical sensing platform coupled with a molecularly imprinted polymer and CuCo2O4/NCNTs signal amplification for selective determination of gemcitabine

A novel and reliable electrochemical analysis tool was developed for gemcitabine (GEM) detection by combining the selective recognition of molecular imprinted polymer (MIP) technology and ratiometric quantification strategy. In this contribution, a glassy carbon electrode (GCE) surface was first modified by drop-coating CuCo2O4/NCNTs and ferrocene (FC) to achieve a ratiometric on-off response (CuCo2O4/NCNTs/FC was served as a substrate to amplify signal and to provide reference signal). Then, MIP network was prepared through in situ electrochemical polymerization, using aniline as monomer and GEM as template. Differential pulse voltammetry (DPV) analysis showed that the oxidation peak signal of FC decreased with the increase of GEM concentration, whereas the oxidation peak signal of GEM increased. Therefore, the peak current ratio of IGEM/IFC was employed to accurately reflect the concentration of GEM. Using this method, GEM was measured in the range from 0.1 to 150 µM with a low limit of detection of 11.3 nM. In addition, the sensor showed high reproducibility, anti-interference ability and good stability for 6 weeks toward GEM detection. Finally, the proposed sensor exhibited excellent detection performance in complex pharmaceutical and biological matrices with satisfactory recoveries.

Determination of drug release profile of doxorubicin encapsulated in SLN with NMR spectroscopy

Solid lipid nanoparticles (SLN) have many various properties such as controlled drug release, elimination of side effects of drugs, etc. In this study, drug release study of SLN formulations was performed with Nuclear Magnetic Resonance (NMR) spectroscopy. Results obtained from NMR experiments were compared with other studies in the literature in which drug release of doxorubicin encapsulated in SLN formulations was carried out using High Pressure Liquid Chromatography (HPLC) and UV-VIS spectrophotometer. In NMR experiments, d6-DMSO and tetra methyl silane (TMS) were used as solvent and internal standard materials, respectively. Moreover, ferrocene was used as internal standard material in qNMR experiments. Doxorubicin was encapsulated in SLNs and after investigating the physicochemical properties of SLN formulations, specificity and selectivity of the qNMR method were evaluated by ratio of S/N ratio (signal/noise ratio) of singlet signal of doxorubicin to ratio of S/N ratio signal of ferrocene (internal standard material). Moreover, accuracy and precision of the qNMR method were evaluated. Results of qNMR method were validated. The results obtained from the qNMR method have been shown to be compatible with the results obtained from other traditional methods such as HPLC, UV-VIS, etc. It was also shown that the qNMR method is a simple and easy method for release of drugs encapsulated in SLNs. As a result, qNMR method is a suitable characterization method for determination of drug release of SLN formulations.

Gold-based nanostructured platforms for oxytetracycline detection from milk by a “signal-on” aptasensing approach

Several gold platforms of different morphologies were investigated in the elaboration of a new aptasensor for oxytetracycline. Au-nanostructures were electrochemically synthesized from solutions of different concentrations of HAuCl4 in different media by chronoamperometry, multipulse amperometry, and chronopotentiometry, respectively at carbon-based screen-printed electrodes (C-SPE). The nano-/micro-scale morphologies of the patterned surfaces and elemental composition were examined by scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy, respectively. The electrochemical properties of the obtained gold nanostructured platforms (AuNSs|C-SPE) were investigated to achieve optimal aptamer coverage. The results showed that the aptasensor developed using the platform with thistle-like AuNSs exhibited the highest conductivity in terms of ferrocene signal and the largest effective area. Under optimal conditions, a linear range from 5.0 × 10−8 M to 1.2 × 10−6 M, with a limit of detection (LOD) of 8.7 × 10−9 M OXT were obtained, which is about 20 times lower than the EU regulations for OXT residues in milk. The electrochemical aptasensor was able to discriminate other antibacterial agents, such as amoxicillin, ampicillin, gentamicin, tetracycline, and vancomycin and was successfully applied in milk samples. This “signal-on” aptasensing approach provides a simple and cost-effective disposable sensor that could be easily applied for the on-site determination of antibiotics.

Duplex Electrochemical DNA Sensor to Detect Bacillus anthracis CAP and PAG DNA Targets Based on the Incorporation of Tailed Primers and Ferrocene-Labeled dATP.

We report the duplex amplification of two plasmid DNA markers involved in the virulence of Bacillus anthracis, CAP and PAG, and the direct electrochemical detection of these amplicons. The method consists of the simultaneous amplification of the two targets in a single-pot reaction via polymerase chain reaction (PCR) using tailed primers and ferrocene-labeled dATP. Following amplification, the PCR products hybridize to probes immobilized on electrodes in a microfabricated electrode array chip. The incorporated ferrocene labeled dATP is then detected using square wave voltammetry. We evaluated the effect of electrolyte cations, anions, and concentration to condense, bend, and shrink double-stranded DNA and their effect on the intensity of the ferrocene signal. We obtained detection limits of 0.8 and 3.4 fM for CAP and PAG targets, respectively. We successfully developed a method to detect the presence of both targets in genomic DNA extracted from real samples.

Electrochemical Aptasensor Based on Sulfur-Nitrogen Codoped Ordered Mesoporous Carbon and Thymine-Hg2+-Thymine Mismatch Structure for Hg2+ Detection.

A renewable electrochemical aptasensor was proposed for super-sensitive determination of Hg2+. The novel aptasensor, based on sulfur-nitrogen codoped ordered mesoporous carbon (SN-OMC) and thymine-Hg2+-thymine (T-Hg2+-T) mismatch structure, used ferrocene as signal molecules to achieve the conversion of current signals. In the absence of Hg2+, the thiol-modified T-rich probe 1 spontaneously formed a hairpin structure by base pairing. After being hybridized with the ferrocene-labeled probe 2 in the presence of Hg2+, the hairpin structure of probe 1 was opened due to the preferential formation of the T-Hg2+-T mismatch structure, and the ferrocene signal molecules approached the modified electrode surface. SN-OMC with high specific surface area and ample active sites acted as a signal amplification element in electrochemical sensing. The sensitive determination of Hg2+ can be actualized by analyzing the relationship between the change of oxidation current caused by ferrocene signal molecules and the Hg2+ concentrations. The aptasensor had a fine linear correlation in the range of 0.001-1000 nM with a detection limit of 0.45 pM. The aptasensor also displayed a good response in real sample detection and provided a promising possibility for in situ detection.

SYNTHESIS OF BIOTINYLATED FERROCENE, AND ITS APPLICATION AS A REDOX PROBE FOR ELECTROCHEMICAL IMMUNOSENSOR

The coupling compound of Biotin (Vitamin H) and redox molecule ferrocene throughcovalent bonding was studied. Synthesis and structure identification of Biotinylated 1 - (- 2-aminoethyl) ferrocene were performed by 1H-NMR, 13C-NMR and MS. The ultimate goal of thispaper is to develop derivatives of ferroceneservingas an electrochemical probe that wouldenhance the performance of immunosensor.An immunosensor based on polypyrrole-streptavidinlayer as platform for immobilization of biotinylatedferrocene and antibodies was developed. Themeasurement of redox signal of ferrocene was analyzed by differential pulse voltammetry(DPV) method and underlined a variation of redox properties upon the antigen interaction. Theintroduction of the redox biotinylatedferrocene into streptavidin-polypyrrole layer affords a goodsensitivity of the biosensor with a detection limit of 0.16 pg.mL-1.

New generation of electrochemical immunoassay based on polymeric nanoparticles for early detection of breast cancer.

Screening and early diagnosis are the key factors for the reduction of mortality rate and treatment cost of cancer. Therefore, sensitive and selective methods that can reveal the low abundance of cancer biomarkers in a biological sample are always desired. Here, we report the development of a novel electrochemical biosensor for early detection of breast cancer by using bioconjugated self-assembled pH-responsive polymeric micelles. The micelles were loaded with ferrocene molecules as “tracers” to specifically target cell surface-associated epithelial mucin (MUC1), a biomarker for breast and other solid carcinoma. The synthesis of target-specific, ferrocene-loaded polymeric micelles was confirmed, and the resulting sensor was capable of detecting the presence of MUC1 in a sample containing about 10 cells/mL. Such a high sensitivity was achieved by maximizing the loading capacity of ferrocene inside the polymeric micelles. Every single event of binding between the antibody and antigen was represented by the signal of hundreds of thousands of ferrocene molecules that were released from the polymeric micelles. This resulted in a significant increase in the intensity of the ferrocene signal detected by cyclic voltammetry.

Decoration of Reduced Graphene Oxide Nanosheets with Aryldiazonium Salts and Gold Nanoparticles toward a Label-Free Amperometric Immunosensor for Detecting Cytokine Tumor Necrosis Factor-α in Live Cells.

In this study, a label-free electrochemical immunosensor was developed for detection of cytokine tumor necrosis factor-alpha (TNF-α). First, AuNPs loaded reduced graphene oxides nanocomposites (RGO-ph-AuNP) were prepared, and then, a mixed layer of 4-carbxyphenyl and 4-aminophenyl phosphorylcholine (PPC) was modified to the surface of AuNPs for the subsequent modification of anti-TNF-α capture antibody (Ab1) to form the capture surface (Au-RGO-ph-AuNP-ph-PPC(-ph-COOH)) for the analyte TNF-α with the antifouling property. For reporting the presence of analyte, the anti-TNF-α detection antibody (Ab2) was modified to the graphene oxides which have been modified with the 4-ferrocenylaniline through diazonium chemistry to form Ab2-GO-ph-Fc. Then, a sandwich assay was formed on gold surfaces for the quantitative detection of TNF-α based on the electrochemical signal of ferrocene. X-ray photoelectron spectra (XPS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), UV-vis, and electrochemistry were used for characterization of the stepwise fabrications on the interface. The prepared electrochemical immunosensor was successfully used for the detection of TNF-α over the range of 0.1-150 pg mL-1. The lowest detection limit of this immunosensor is 0.1 pg mL-1 TNF-α in 50 mM phosphate buffer at pH 7.0. The fabricated immunosensor provided high selectivity and stability and can be used to detect TNF-α secreted by live BV-2 cells with comparable accuracy to enzyme-linked immunosorbent assay (ELISA) but with lower limit of detection.

Streptavidin‐polypyrrole Film as Platform for Biotinylated Redox Probe Immobilization for Electrochemical Immunosensor Application

AbstractA platform for construction of multi‐array electrochemical immunosensors was developed in which the measurement could be performed by various targets depending on the potential ranges of electrochemical detection. This was demonstrated by the immobilization of biotinylated redox molecules such as viologen and ferrocene, on modified polypyrrole‐streptavidin film. The polypyrrole film was modified by streptavidin layer, which serves for both the attachment of biotinylated redox marker and biotinylated antibody. Such biologically modified surface exhibits variation of electrochemical response of redox molecule at various potential ranges after antibody/antigen interaction. The measurement of redox signal of viologen and ferrocene was analyzed by differential pulse voltammetry (DPV) method and underlines a variation of redox properties upon the antigen interaction. Viologen immobilized on polypyrrole /streptavidin surface shows a redox signal at −1.2 V versus Ag/AgCl corresponding to the reduction of dicationic viologen to neutral viologen within 2 electrons process. Immobilized biotinylated ferrocene exhibits redox signal at 0.4 V versus Ag/AgCl. We demonstrate that when the biolayer bearing antibody is in contact with antigen, the redox signal of ferrocene or viologen was modified. The variation of current signal is directly related to the concentration of antigen in solution. A detection limit of pg.mL−1 was obtained demonstrating the sensitivity of such electrochemical immunosensor. The modified streptavidin polypyrrole surface bearing various biotinylated redox markers is a proof of concept for multi‐array electrochemical detection system of complex sample.

Electrochemical functionalization of polypyrrole through amine oxidation of poly(amidoamine) dendrimers: Application to DNA biosensor

Electrochemical patterning method has been developed to fabricate composite based on polypyrrole (PPy) film and poly(amidoamine) dendrimers of fourth generation (PAMAM G4). PPy layer was generated using electrochemical polymerization of pyrrole on a gold electrode. PPy film was then modified with PAMAM G4 using amines electro-oxidation method. Covalent bonding of PAMAM G4 and the formation of PPy-PAMAM composite was characterized using Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray Photoelectron Spectroscopy (XPS). Ferrocenyl groups were then attached to such surface as a redox marker. Electrochemical properties of the modified nanomaterial (PPy-PAMAM-Fc) were studied using both amperometric and impedimetric methods to demonstrate the efficiency of electron transfer through the modified PPy layer. The obtained electrical and electrochemical properties were compared to a composite where PPy bearing carboxylic acid functions was chemically modified with PAMAM G4 by covalent attachment through formation of amid bond (PPy-CONH-PAMAM). The above mentioned studies showed that electrochemical patterning does not disturb the electronic properties of PPy. The effect of the number of functional groups introduced by the electrochemical patterning was demonstrated through the association of various compounds (ethylenediamine, PAMAM G2 and PAMAM G6). We demonstrated that such compounds could be applied in the biosensors technology. The modified PPy-PAMAM-Fc was evaluated as a platform for DNA sensing. High performance in the DNA detection by variation of the electrochemical signal of ferrocene was obtained with detection limit of 0.4 fM. Furthermore, such approach of electrochemical patterning by oxidation of amines could be applied for chemical modification of PPy and open a new way in various biosensing application involving functionalized PPy.

Amplified inhibition of the electrochemical signal of ferrocene by enzyme-functionalized graphene oxide nanoprobe for ultrasensitive immunoassay

A nanoprobe-induced signal inhibition mechanism was designed for ultrasensitive electrochemical immunoassay at a chitosan-ferrocene (CS-Fc) based immunosensor. The nanoprobe was prepared by covalently loading signal antibody and high-content horseradish peroxidase (HRP) on the graphene oxide (GO) nanocarrier. The immunosensor was prepared through the stepwise assembly of gold nanoparticles (Au NPs) and capture antibody at a CS-Fc modified electrode. After sandwich immunoreaction, the GO-HRP nanoprobes were quantitatively captured onto the immunosensor surface and thus induced the production of a layer of insoluble film through the enzymatically catalytic reaction of the HRP labels. Both the dielectric immunocomplex formed on the immunosensor surface and the enzymatic precipitate with low electroconductivity led to the electrochemical signal decease of the Fc indicator, which was greatly amplified by the multi-enzyme signal amplification of the nanoprobe. Based on this amplified signal inhibition mechanism, a new ultrasensitive electrochemical immunoassay method was developed. Using carcinoembryonic antigen as a model analyte, this method showed a wide linear range over 5 orders of magnitude with a detection limit down to 0.54 pg/mL. Besides, the immunosensor showed good specificity, acceptable reproducibility and stability as well as satisfactory reliability for the serum sample analysis.

E-DNA sensor of Mycobacterium tuberculosis based on electrochemical assembly of nanomaterials (MWCNTs/PPy/PAMAM).

Two-step electrochemical patterning methods have been employed to elaborate composite nanomaterials formed with multiwalled carbon nanotubes (MWCNTs) coated with polypyrrole (PPy) and redox PAMAM dendrimers. The nanomaterial has been demonstrated as a molecular transducer for electrochemical DNA detection. The nanocomposite MWCNTs-PPy has been formed by wrapping the PPy film on MWCNTs during electrochemical polymerization of pyrrole on the gold electrode. The MWCNTs-PPy layer was modified with PAMAM dendrimers of fourth generation (PAMAM G4) with covalent bonding by electro-oxidation method. Ferrocenyl groups were then attached to the surface as a redox marker. The electrochemical properties of the nanomaterial (MWCNTs-PPy-PAMAM-Fc) were studied using both square wave voltammetry and cyclic voltammetry to demonstrate efficient electron transfer. The nanomaterial shows high performance in the electrochemical detection of DNA hybridization leading to a variation in the electrochemical signal of ferrocene with a detection limit of 0.3 fM. Furthermore, the biosensor demonstrates ability for sensing DNA of rpoB gene of Mycobacterium tuberculosis in real PCR samples. Developed biosensor was suitable for detection of sequences with a single nucleotide polymorphism (SNP) T (TCG/TTG), responsible for resistance of M. tuberculosis to rifampicin drug, and discriminating them from wild-type samples without such mutation. This shows potential of such systems for further application in pathogens diagnostic and therapeutic purpose.

An electrochemiluminescent DNA sensor based on nano-gold enhancement and ferrocene quenching

An electrochemiluminescent DNA (ECL-DNA) sensor based on nano-gold signal enhancement (i.e. gold nanoparticles, GNP) and ferrocene signal quenching was investigated. The Au electrode was first modified with GNPs through electrodeposition method, followed by subsequent immobilization of single-stranded probe DNA labeled with ruthenium complex. The resulting sensor produced a higher ECL signal due to its higher density of self-assembled probe DNAs on the surface. Upon the hybridization of probe DNA with complementary target DNA labeled with ferrocene, ECL intensity decreased significantly due to spatial separation of ECL label from the electrode surface. As a result, the ECL signal was simultaneously quenched by ferrocene. The effects of both nano-gold electrodeposition time and ferrocene on the performance of ECL-DNA sensor were studied in detail and possible reasons for these effects were suggested as well. The reported ECL-DNA sensor showed great sensitivity and may provide an alternative approach for DNA detection in diagnostics and gene analysis.

Electrochemical signal modulation in homogeneous solutions using the formation of an inclusion complex between ferrocene and β-cyclodextrin on a DNA scaffold

Two DNA conjugates modified with ferrocene and β-cyclodextrin were prepared as a pair of probes that work cooperatively for DNA sensing, in which the electrochemical signal of ferrocene on one probe was significantly "quenched" by the formation of an inclusion complex with β-cyclodextrin of the other probe on the DNA templates.

Target label-free, reagentless electrochemical DNA biosensor based on sub-optimum displacement

One of the most time consuming and complex steps in the detection of DNA target with a biosensor is the previous labeling of the target. In this paper, a novel target label-free, reagentless and easy to use DNA biosensor is reported. Electrochemical transduction (cyclic voltammetry, differential pulse voltammetry and impedance spectroscopy) and optical red out by surface plasmon resonance were chosen for the platform optimization. This target label-free DNA detection method is based on displacement of sub-optimum labeled oligonucleotide. This strategy requires the pre-hybridization of the capture probe immobilized on the electrode surface with a sub-optimum mutated oligonucleotide pre-labeled with an electrochemically active ferrocene moiety. Due to the higher affinity of the target that is fully complementary to the capture probe, the sub-optimum ferrocene-labeled sequence is displaced when the fully complementary target is introduced into the system. The decrease of the electrochemical signal from the ferrocene verifies the presence of the target, which is proportional to the target concentration. A variation of this strategy was employed to enhance the ferrocene signal. A diffusional mediator, ferrocyanide, was introduced in the system to help in this purpose. This platform attains a stable, specific and reproducible response (5–15%), with a detection limit in the range of μM. This electrochemical sensor is the first example of this kind of sensor to detect cystic fibrosis, however, this configuration could be generically applied to any application where the detection of a DNA target is involved.