Determination of apple juice authenticity using gas chromatography-mass spectrometry, volt-ampere and new conductometric methods.

BACKGROUND: Organoleptic properties and positive health effect on consumers both justify the importance of determining apple juice authenticity with respect to retail and wholesale trade networks worldwide. RESULTS: Adulteration of apple juice through dilution with water, as well as with ascorbic acid, has been determined. It has been demonstrated that polarization curves of a platinum electrode in apple juice are useful for undeclared antioxidant determination, as a result of the movement of the polarization curve to the left, by 200 mV, when ascorbic acid was added. A difference between the equivalent electrical conductivity of suspended solids of undiluted and diluted (1:1) juices has been substantiated as a new quantitative criterion for determining adulteration through dilution. The criterion values range from 0.030 to 0.034 S m-1 for juices of different apple varieties. Gas chromatography-mass spectrometry results have shown the presence of (E)-2-hexenal and n-hexanal in all juices tested obtained from different apple varieties. CONCLUSION: A new conductometric method for the determination of diluted apple juices has been substantiated. It has been established that the volt-ampere method is useful for the investigation of undeclared ascorbic acid. © 2018 Society of Chemical Industry.

Ultrasensitive photoelectrochemical biosensor for the detection of HTLV-I DNA: A cascade signal amplification strategy integrating λ-exonuclease aided target recycling with hybridization chain reaction and enzyme catalysis.

Sensitive and specific detection of DNA is of great significance for clinical diagnosis. In this paper, an effective cascade signal amplification strategy was introduced into photoelectrochemical (PEC) biosensor for ultrasensitive detection of human T-cell lymphotropic virus type I (HTLV-I) DNA. This proposed signal amplification strategy integrates λ-exonuclease (λ-Exo) aided target recycling with hybridization chain reaction (HCR) and enzyme catalysis. In the presence of target DNA (tDNA) of HTLV-I, the designed hairpin DNA (h1DNA) hybridized with tDNA, subsequently recognized and cleaved by λ-Exo to set free tDNA. With the λ-Exo aided tDNA recycling, an increasing number of DNA fragments (output DNA, oDNA) were released from the digestion of h1DNA. Then, triggered by the hybridization of oDNA with capture DNA (cDNA), numerous biotin-labeled hairpin DNAs (h2DNA and h3DNA) could be loaded onto the photoelectrode via the HCR. Finally, avidin-labeled alkaline phosphatase (avidin-ALP) could be introduced onto the electrode by specific interaction between biotin and avidin. The ALP could catalyze dephosphorylation of phospho-L-ascorbic acid trisodium salt (AAP) to generate an efficient electron donor of ascorbic acid (AA), and thereby greatly increasing the photocurrent signal. By utilizing the proposed cascade signal amplification strategy, the fabricated PEC biosensor exhibited an ultrasensitive and specific detection of HTLV-I DNA down to 11.3 aM, and it also offered an effective strategy to detect other DNAs at ultralow levels.

A sandwich-type electrochemical immunoassay for ultrasensitive detection of non-small cell lung cancer biomarker CYFRA21-1.

Many studies confirm that the aberrant expression of Cytokeratin 19 fragment 21-1 (CYFRA21-1) is highly correlated with non-small cell lung cancer (NSCLC), especially for squamous cell carcinoma. Herein, we report a sandwich-type electrochemical immunosensor based on signal amplification strategy of multiple nanocomposites to test CYFRA21-1 selectively and sensitively. The proposed immunosensor fabricated by three-dimensional graphene (3D-G), chitosan (CS) and glutaraldehyde (GA) composite on the glass carbon electrode (GCE) with a large surface area is prepared to immobilize primary antibodies (Ab1) and provide excellent conductivity. To further amplify the electrochemical signal, the trace tag on the foundation of gold nanoparticles (AuNPs) is coated with amino-functionalized carbon nanotube (MWCNT-NH2) nanocomposite through thionine linking, which provides more amino groups to capture more horseradish peroxidase-labeled antibodies (HPR-Ab2) and enhances the conductivity. Under optimal conditions, the developed immunosensor exhibits excellent analytical performance for the determination of CYFRA21-1 with a wide linear range from 0.1 to 150ng·mL-1 and a low detection limit (LOD) of 43pg·mL-1. Furthermore, satisfactory results are obtained for the determination of CYFRA21-1 in real clinical serum samples, indicating the potential of the immunoassay to be applied in clinical analysis.

The Analgesic Acetaminophen and the Antipsychotic Clozapine Can Each Redox-Cycle with Melanin.

Melanins are ubiquitous but their complexity and insolubility has hindered characterization of their structures and functions. We are developing electrochemical reverse engineering methodologies that focus on properties and especially on redox properties. Previous studies have shown that melanins (i) are redox-active and can rapidly and repeatedly exchange electrons with diffusible oxidants and reductants, and (ii) have redox potentials in midregion of the physiological range. These properties suggest the functional activities of melanins will depend on their redox context. The brain has a complex redox context with steep local gradients in O2 that can promote redox-cycling between melanin and diffusible redox-active chemical species. Here, we performed in vitro reverse engineering studies and report that melanins can redox-cycle with two common redox-active drugs. Experimentally, we used two melanin models: a convenient natural melanin derived from cuttlefish (Sepia melanin) and a synthetic cysteinyldopamine-dopamine core-shell model of neuromelanin. One drug, acetaminophen (APAP), has been used clinically for over a century, and recent studies suggest that low doses of APAP can protect the brain from oxidative-stress-induced toxicity and neurodegeneration, while higher doses can have toxic effects in the brain. The second drug, clozapine (CLZ), is a second generation antipsychotic with polypharmacological activities that remain incompletely understood. These in vitro observations suggest that the redox activities of drugs may be relevant to their modes-of-action, and that melanins may interact with drugs in ways that affect their activities, metabolism, and toxicities.

Novel synthesis and characterization of pristine Cu nanoparticles for the non-enzymatic glucose biosensor.

Non enzymatic electrochemical glucose sensing was developed based on pristine Cu Nanopartilces (NPs)/Glassy Carbon Electrode (GCE) which can be accomplished by simple green method via ocimum tenuiflorum leaf extract. Then, the affect of leaf extract addition on improving Structural, Optical and electrochemical properties of pristine cu NPs was investigated. The synthesized Cu NPs were characterized with X-ray diffraction (X-ray), Uv-Visible spectroscopy (Uv-Vis), Fourier transformation infrared spectroscopy (FTIR), Particle size distribution (PSA), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), Transmission electron microscopy (TEM) for structural optical and morphological studies respectively. The synthesized Cu NPs were coated over glassy carbon electrode (GCE) to study the electrochemical response of glucose by cyclic voltammetry and ampherometer. The results indicates that the modified biosensor shows a remarkable sensitivity (1065.21 µA mM-1 cm-2), rapid response time (<3s), wide linear range (1 to 7.2 mM), low detection limit (0.038 µM at S/N = 3). Therefore, the prepared Cu NPs by the Novel Bio-mediated route were exploited to construct a non-enzymatic glucose biosensor for sustainable clinical field applications.

Construction of novel electrochemical immunosensor for detection of prostate specific antigen using ferrocene-PAMAM dendrimers.

In this study, an immunosensor was designed to utilize for the detection of prostate specific antigen (PSA) based on three different generations (G1, G2 and G3) of ferrocene (Fc) cored polyamidiamine dendrimers (Fc-PAMAM) gold (Au) electrode. The self-assembled monolayer principle (SAM) was used to fabricate the sensitive, selective and disposable immunosensor electrodes. In electrode fabrication cysteamine (Cys) was the first agent covalently linked on the Au electrode surface. Immobilized redox center (ferrocene) cored PAMAM dendrimers served as a layer for the further binding of biological components. The monoclonal antibody of PSA (anti-PSA) was covalently immobilized on dendrimers which were attached onto the modified Au surface (Au/Cys/Fc-PAMAMs/anti-PSA). PSA levels were quantitatively analyzed by using electrochemical differential pulse voltammetry (DPV) whose lowest detection limit was calculated as 0.001ngmL(-1). The Au/Cys/FcPAMAM/anti-PSA immunosensor showed excellent performance for PSA at the pulse amplitude; 50mV and the scan rate; 10mV/s in a wide linear concentration range of 0.01ng-100ngmL(-1). Analytical performance and specificity assays were carried out using human serum and different proteins.

Simultaneous determination of 6-mercaptopruine, 6-thioguanine and dasatinib as three important anticancer drugs using nanostructure voltammetric sensor employing Pt/MWCNTs and 1-butyl-3-methylimidazolium hexafluoro phosphate.

6-Mercaptopurine, 6-thioguanine and dasatinib are three important anticancer drugs with high adverse effects in human body. In this study, a Pt/MWCNTs-1-butyl-3-methylimidazolium hexafluoro phosphate-modified carbon paste electrode was developed for the simultaneously determination of 6-mercaptopurine, 6-thioguanine and dasatinib for the first time. The Pt/MWCNTs synthesized by polyol method and have been characterized by transmission electron microscopy and X-ray diffraction methods. The obtained data revealed that the electro-oxidation of 6-mercaptopurine, 6-thioguanine and dasatinib is facilitated as a novel voltammetric sensor. After optimization of electrochemical parameters employing this sensor at pH 8.0, the oxidation peak currents for 6-mercaptopurine, 6-thioguanine and dasatinib were found to vary linearly with their concentrations in the range of 0.05-550µM; 0.1-500µM and 5.0-500µM with detection limits of 0.009µM, 0.05µM and 1.0µM respectively using square wave voltammetric method. The modified electrode has been applied for the selective and precise analysis of 6-mercaptopurine, 6-thioguanine and dasatinib in pharmaceutical formulations and urine samples.

A superstructure-based electrochemical assay for signal-amplified detection of DNA methyltransferase activity.

DNA methyltransferase (MTase) activity is highly correlated with the occurrence and development of cancer. This work reports a superstructure-based electrochemical assay for signal-amplified detection of DNA MTase activity using M.SssI as an example. First, low-density coverage of DNA duplexes on the surface of the gold electrode was achieved by immobilized mercaptohexanol, followed by immobilization of DNA duplexes. The duplex can be cleaved by BstUI endonuclease in the absence of DNA superstructures. However, the cleavage is blocked after the DNA is methylated by M.SssI. The DNA superstructures are formed with the addition of helper DNA. By using an electroactive complex, RuHex, which can bind to DNA double strands, the activity of M.SssI can be quantitatively detected by differential pulse voltammetry. Due to the high site-specific cleavage by BstUI and signal amplification by the DNA superstructure, the biosensor can achieve ultrasensitive detection of DNA MTase activity down to 0.025U/mL. The method can be used for evaluation and screening of the inhibitors of MTase, and thus has potential in the discovery of methylation-related anticancer drugs.

Electrochemical detection of Nanog in cell extracts via target-induced resolution of an electrode-bound DNA pseudoknot.

Nanog is among the most important indicators of cell pluripotency and self-renew, so detection of Nanog is critical for tumor assessment and monitoring of clinical prognosis. In this work, a novel method for Nanog detection is proposed by using electrochemical technique based on target-induced conformational change of an electrode-bound DNA pseudoknot. In the absence of Nanog, the rigid structure of the pseudoknot will minimize the connection between the redox tag and the electrode, thus reducing the obtained faradaic current. Nevertheless, the Nanog binding may liberate the flexible single-stranded element that transforms the DNA pesudokont into DNA hairpin structure due to steric hindrance effect, thus making the electrochemical tag close to the electrode surface. Consequently, electron transfer can be enhanced and very well electrochemical response can be observed. By using the proposed method, Nanog can be determined in a linear range from 2nM to 25nM with a detection limit of 163 pM. Furthermore, the proposed method can be directly used to assay Nanog not only in purified samples but also in complex media (cell extracts), which shows potential applications in Nanog functional studies as well as clinical diagnosis in the future.

Dual-responsive immunosensor that combines colorimetric recognition and electrochemical response for ultrasensitive detection of cancer biomarkers.

We developed a nanoroughened, biotin-doped polypyrrole immunosensor for the detection of tumor markers through dual-signal (electrochemical and colorimetric) channels, electrochemical and colorimetric, that demonstrates remarkable analytical performance. A rapid, one-step electric field-mediated method was employed to fabricate the immunosensor with nanoscale roughness by simply modulating the applied electrical potential. We demonstrated the successful detection of three tumor markers (CA125, CEA, and PSA) via the double enzymatic signal amplifications in the presence of a target antigen, ultimately leading to desired diagnostic accuracy and reliability. The addition of multiple horseradish peroxidase (HRP)- and antibody-labeled nanoparticles greatly amplified the signal and simplified the measurement of cancer biomarker proteins by sequentially magnifying electrochemical and colorimetric signals in a single platform. The two parallel assays performed using the proposed immunosensor have yielded highly consistent and reproducible results. Additionally, for the analysis of plasma samples in a clinical setting, the values obtained with our immunosensor were validated by correlating the results with those of a standard radioimmunoassay (RIA), which obtained very similar clinically valid responses.

A Comprehensive Review of Gas Sensors Using Carbon Materials.

In recent years, interest in carbon materials for use in gas sensors has increased. Carbon materials have unique electrical, optical and mechanical properties, making these materials very interesting. In this review, the properties of carbon materials are first introduced. Surface modification for carbon materials, fabrication for gas sensors, and the gas-sensing conditions and mechanisms according to the different types of carbon materials are chiefly described. In particular, this review focuses on the enhancement of the gas-sensing properties of carbon materials depending on the modification methods used and its mechanism.

Pt NPs and DNAzyme functionalized polymer nanospheres as triple signal amplification strategy for highly sensitive electrochemical immunosensor of tumour marker.

Highly sensitive determination of tumour markers is the key for early diagnosis of cancer. Herein, triple signal amplification strategy resulting from polymer nanospheres, Pt NPs, and DNAzyme was proposed in the developed electrochemical immunosensor. First, electroactive polymer nanospheres were synthesized by infinite coordination polymerization of ferrocenedicarboxylic acid, which could generate strong electrochemical signals due to plentiful ferrocene molecules. Further, the polymer nanospheres were functionalized by Pt NPs and DNAzyme (hemin/G-quadruplex) with the ability of catalyzing H2O2, which contributes to enhance the electrochemical signals. The prepared conjugations were characterized by transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy (EDX). And the process of preparation was monitored by zeta potential. Based on the sandwich-type immunoassay, the electrochemical immunosensor was constructed employing the conjugations as signal tags. Under optimal conditions, the DPV peak increased with the increasing of alpha fetal protein (AFP) concentration, and the linear range was from 0.1pgmL(-1) to 100ngmL(-1) with low detection limit of 0.086pgmL(-1). Meanwhile, the designed immunosensor exhibited excellent selectivity and anti-interference property, good reproducibility and stability. More importantly, there were no significant differences in analyzing real clinical samples between designed immunosensor and commercial ELISA.

8-hydroxy-2'-deoxyguanosine (8-OHdG) biomarker detection down to picoMolar level on a plastic antibody film.

An innovative biosensor assembly relying on a simple and straightforward in-situ construction is presented to monitor urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) down to the pmol/L level. The sensing film of the biosensor consisted of a molecularly imprinted polymer (MIP) layer for 8-OHdG assembled on a gold electrode through electropolymerization of monomer combined with the template. The analytical features of the resulting biosensor were assessed by Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). Some experimental parameters such as the initial concentration of the monomer and the ratio template-monomer were investigated and optimized in order to finely tune the performance of the MIP-based sensor. Under optimal conditions, the developed biosensor was able to rebind 8-OHdG with a linear response against EIS from 0.1 to 100pg/ml 3.5-3500 pM. The interference of coexisting species was tested, also with calibrations on urine samples, and good selectivity towards 8-OHdG was obtained. RAMAN spectroscopy, FTIR and SEM evaluations of the prepared films confirmed the formation of a polyphenol thin-film on the electrode surface. The presence and distribution of the imprinted cavities on the MIP layer was confirmed by confocal microscopy imaging of the film, after a post-treatment with Fluorescein Isothiocyanate (FITC) labeled 8-OHdG antibody. Overall, this label-free biosensor for urinary 8-OHdG detection constitutes a promising low-cost alternative to the conventional immunoassay approaches, due to its simplicity, stability, high sensitivity and selectivity for biological sample assays, opening new doors for other applications.

Electrochemical monitoring-on-chip (E-MoC) of HIV-infection in presence of cocaine and therapeutics.

Electrochemical monitoring-on-chip (E-MoC)-based approach for rapid assessment of human immunodeficiency virus (HIV)-infection in the presence of cocaine (Coc) and specific drugs namely i.e., tenofovir (Tef), rimcazole (RA) is demonstrated here, for the first time, using electrochemical impedance spectroscopy (EIS). An in-vitro primary human astrocytes (HA) model was developed using a cultureware chip (CC, used for E-MoC) for HIV-infection, Coc exposure and treatment with anti-HIV drug i.e., Tef, and Coc antagonist i.e., RA. The charge transfer resistance (Rct) value of each CC well varies with respect to infection and treatment demonstrated highly responsive sensitivity of developed chip. The results of E-MoC, a proof-of-the concept, suggested that HIV-infection progression due to Coc ingestion and therapeutic effects of highly specific drugs are measurable on the basis of cell electrophysiology. Though, this work needs various molecular biology-based optimizations to promote this technology as an analytical tool for the rapid assessment of HIV-infection in a patient to manage HIV diseases for timely diagnosis. The presented study is based on using CNS cells and efforts are being made to perform this method using peripheral cells such as monocytes derived dendritic cells.

Visible light photoelectrochemical aptasensor for adenosine detection based on CdS/PPy/g-C3N4 nanocomposites.

In this work, a label-free photoelectrochemical (PEC) aptasensor was developed for adenosine detection based on CdS/PPy/g-C3N4 nanocomposites. The CdS/g-C3N4 heterojunction effectively prevented the photogenerated charges recombination of g-C3N4 and self-photocorrosion processes of CdS, improving photo-to-current conversion efficiency. The introduced polypyrrole (PPy) nanoparticles could lead to a more effective separation of photogenerated charges, thus resulting in a further increasing of photocurrent. The CdS/PPy/g-C3N4 was firstly employed as the photoactive materials for fabrication of aptasensor, and SH-aptamer was then adsorbed on the CdS/PPy/g-C3N4 modified electrodes through S-Cd bond. With increasing of adenosine concentration, the photocurrent decreased as the formation of SH-aptamer-adenosine bioaffinity complexes. Under optimal conditions, the PEC aptasensor had a sensitive response to adenosine in a linear range of 0.3nmolL(-1) to 200nmolL(-1) with a detection limit of 0.1nmolL(-1). Besides, the as-proposed aptasensor has also been applied in human serum samples analysis. The aptasensor exhibits high sensitivity and good stability, thus opening up a new promising PEC platform for some other small molecules analysis.

Single-walled carbon nanotubes covalently functionalized with polytyrosine: A new material for the development of NADH-based biosensors.

We report for the first time the use of single-walled carbon nanotubes (SWCNT) covalently functionalized with polytyrosine (Polytyr) (SWCNT-Polytyr) as a new electrode material for the development of nicotinamide adenine dinucleotide (NADH)-based biosensors. The oxidation of glassy carbon electrodes (GCE) modified with SWCNT-Polytyr at potentials high enough to oxidize the tyrosine residues have allowed the electrooxidation of NADH at low potentials due to the catalytic activity of the quinones generated from the primary oxidation of tyrosine without any additional redox mediator. The amperometric detection of NADH at 0.200V showed a sensitivity of (217±3)µAmM(-1)cm(-2) and a detection limit of 7.9nM. The excellent electrocatalytic activity of SWCNT-Polytyr towards NADH oxidation has also made possible the development of a sensitive ethanol biosensor through the immobilization of alcohol dehydrogenase (ADH) via Nafion entrapment, with excellent analytical characteristics (sensitivity of (5.8±0.1)µAmM(-1)cm(-2), detection limit of 0.67µM) and very successful application for the quantification of ethanol in different commercial beverages.

Spatial-resolved electrochemiluminescence ratiometry based on bipolar electrode for bioanalysis.

Herein, a spatial-resolved electrochemiluminescene (ECL) ratiometry based on a closed biopolar electrode (BPE) is reported for the highly sensitive detection of prostate specific antigen (PSA). Au@g-C3N4 NCs as one ECL emitter were firstly coated on the cathode of BPE, while the anode of the BPE served for calibration via another ECL substance, Ru(bpy)3(2+). The electroneutrality across the BPE makes the reactions on each pole of BPE electrically coupled. Thus one electrochemical sensing reaction at one pole of BPE could be quantified at both ends. A composite, Pt-PAMAM-DNAzyme was assembled on the surface of cathode via DNA hybridization between probe DNA and PSA aptamer. It acted as an ECL quencher of g-C3N4 via resonance energy transfer (RET) and catalyzing the reduction of O2, the co-reactant of g-C3N4. Meanwhile, it could promote the ECL of Ru(bpy)3(2+) at anode, since the catalytic reduction of O2 at the cathode increased the faradiac current flowing through the BPE. Based on this signal composite, an ECL "off-on" phenomenon was observed at the cathode, after Pt-PAMAM-DNAzyme was "peeled off" by PSA. Conversely, at the anode, an "on-off" ECL changing was obtained. Therefore, a sensitive ratiometry for PSA detection was achieved with a linear range from 0.10 to 200ng/mL. Since the two ECL emitters were physically separated, the ratiometric system was relatively simple and neither optical filters nor spectrometer were required. The strategy combining the ECL ratiometry and BPE broadens the applications of BPE-ECL and shows good perspective in clinical application.

An ultrasensitive electrochemiluminescence sensor based on reduced graphene oxide-copper sulfide composite coupled with capillary electrophoresis for determination of amlodipine besylate in mice plasma.

A new electrochemiluminescence (ECL) sensor based on reduced graphene oxide-copper sulfide (rGO-CuS) composite coupled with capillary electrophoresis (CE) was constructed for the ultrasensitive detection of amlodipine besylate (AML) for the first time. In this work, rGO-CuS composite was synthesized by one-pot hydrothermal method and used for electrode modification. The electrochemical and ECL behaviors of the sensor were investigated. More than 5-fold enhance in ECL intensity was observed after modified with rGO-CuS composite. The results can be ascribed to the presence of rGO-CuS composite on the electrode surface that facilitates the electron transfer rate between the electroactive center of Ru(bpy)3(2+) and the electrode. The ECL sensor was coupled with CE to improve the selectivity and the CE-ECL parameters that affect separation and detection were optimized. Under the optimum conditions, the linear ranges for AML was 0.008-5.0µg/mL with a detection limit of 2.8ng/mL (S/N=3). The method displayed the advantages of high sensitivity, good selectivity, wide linear range, low detection limit and fine reproducibility, and was used to analyze AML in mice plasma with a satisfactory result, which holds a great potential in the field of pharmaceutical analysis.

An electrochemical biosensor for double-stranded Wnt7B gene detection based on enzymatic isothermal amplification.

Wnt7B gene plays an important role in the development and progression of breast cancer, gastric cancer, esophageal cancer and pancreatic cancer. While, the natural state of DNA is double stranded, which makes it difficult to be directly detected. Here, we develop an electrochemical biosensor method for Wnt7B gene detection without the need to denature the target. This method firstly used nicking enzyme for exploiting in the double-stranded DNA (dsDNA). Then, long single-stranded DNA (ssDNA) was generated from the cutting site through polymerase extension reaction. Whereafter, the long ssDNA triggered a hairpin self-assembly recycling reaction, which gave rise to another isothermal amplification reaction. Last, short ssDNA was formed after the this amplification process, which could hybridize with the capture probe immobilized on Au electrode and result in signal variation. This method showed excellent analytical performance for dsDNA, of which the linear range was 2fM to 500pM and the detection limit was 1.6fM (S/N=3). It also showed an good results when applied to the real sample of Wnt7B gene detection.

Gold nanoparticles and polyethylene glycols functionalized conducting polyaniline nanowires for ultrasensitive and low fouling immunosensing of alpha-fetoprotein.

An ultrasensitive biosensor for alpha-fetoprotein was developed based on electrochemically synthesized polyaniline (PANI) nanowires, which were functionalized with gold nanoparticles (AuNPs) and polyethylene glycols (PEG). The prepared PEG/AuNPs/PANI composite, combining the electrical conductivity of the AuNPs/PANI with the robust antifouling ability of PEG, offered an ideal substrate for the development of low fouling electrochemical biosensors. Alpha-fetoprotein (AFP), a well-known hepatocellular carcinoma biomarker, was used as a model analyte, and its antibody was immobilized on the PEG/AuNPs/PANI for the construction of the AFP immunosensor. Using the redox current of PANI as the sensing signal, in addition to the good biocompatibility of PEG/AuNPs and the anti-biofouling property of PEG, the developed immunosensor showed improved biosensing performances, such as wide linear range and ultralow detection limit (0.007pgmL(-1)). More importantly, it is label-free, reagentless and low fouling, making it capable of assaying AFP in real serum samples without suffering from significant interference or biofouling.