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G protein‐coupled cell surface receptors (GPCR) trigger complex intracellular signaling cascades upon agonist binding. Classic pharmacological assays provide information about binding affinities, activation or blockade at different stages of the signaling cascade, but real time dynamics and reversibility of these processes remain often disguised. We show that combining photochromic NPY receptor ligands, which can be toggled in their receptor activation ability by irradiation with light of different wavelengths, with whole cell label‐free impedance assays allows observing the cell response to receptor activation and its reversibility over time. The concept demonstrated on NPY receptors may be well applicable to many other GPCRs providing a deeper insight into the time course of intracellular signaling processes. [ABSTRACT FROM AUTHOR]

In the present paper, symmetrical configuration of dual material double gate dielectric modulated junctionless TFET (DM DG JLTFET) for biosensor applications is explored. The JLTFET consists of Si material with an intensely doped n-type substrate. In this work, the JLTFET utilizes the dielectric modulation method which aids the bio-transistor to recognize neutral and charged analytes (biomolecules). A double metal gate structure is designed by employing two dissimilar metal gate electrodes to reduce short channel impact on device characteristics. The proposed device includes a nanogap region (cavity) which is framed for biomolecules to immobilize. Surface potential and their sensitivity are examined for neutral and charged-neutral analytes. The effects of structure parameters such as nanogap region length and fill-in factor have been analyzed through simulation. The paper examines the behavior of DM DG JLTFET for biological molecules sensing via change in relative permittivity and charge density. The proposed device shows noticeable sensitivity results for charged biomolecules (especially for positively charged analytes). The present work has analyzed the different parameters affecting the sensitivity of the biosensor which includes structural geometric variations like change in cavity length, cavity thickness and fill-in factor. The sensitivity of the neutral biomolecules having higher dielectric constant is observed higher; the surface potential sensitivity of the Gelatin (k = 12) is estimated as 3.75 × 10 3 which is 45%, 55%, and 135% higher than the sensitivity of Keratin (k = 7), Bacteriophage T7 (k = 6), and Glucose Oxidase (k = 3), respectively at the cavity length of 7 nm. [ABSTRACT FROM AUTHOR]

In this paper, a high‐sensitivity refractive index sensor based on a hybrid plasma waveguide and metal–insulator–metal waveguide combined third‐order runway series mosaic microring resonator is proposed. In this structure, a GaAs waveguide ring surrounds a gold waveguide ring in the middle, and the innermost layer is a disk made of gold material. The outer groove waveguide is composed of GaAs‐air‐alloy, and the inner groove waveguide is made of the Gold‐Air‐Gold material disc. By filling different substances in the groove, the change of refractive index will affect the optical signal strength of the output spectrum. The finite element method simulates the transmission spectrum and electric field distribution of the sensor structure. The amplitude coupling coefficient and attenuation factor affecting the resonator's performance are analyzed, and the structural parameters of the slot waveguide are optimized. The numerical simulation results show that the sensor quality factor of this structure is 1.54 × 104, the sensitivity is 1.2 × 103 nm/RIU which is about 1.5 times higher than that of the Si ring with the same structure, the detection limit can reach 8.1892 × 10−7 RIU, and the free spectral range can reach 109 nm. Compared with the traditional microring structure, this microring has higher design freedom and free spectral range and is more suitable for producing biosensors with high sensitivity, low detection limit, and multi‐parameter measurement. [ABSTRACT FROM AUTHOR]

In this work gate-on-drain L-shaped channel Tunnel FET is proposed to detect various biomolecules through label-free bio-sensing detection technique. Biomolecules can be detected in the proposed structure through modulation of ambipolar current between channel and drain. Modulation of ambipolar current is performed by extending gate over drain in order to create a gate to drain overlap (cavity) by etching the specific portion of the gate. Trapped biomolecules within cavity gets immobilized. Immobilized biomolecules change the drain to channel tunneling width, thus changing the ambiploar leakage current. Drain doping and cavity length was fine-tuned to achieve better sensitivity in terms of ambipolar current and ambipolar knee voltage shift with and without presence of biomolecules. A maximum sensitivity of 3.8 × 107 is achieved for drain doping of 5 × 1019 donors/cm3 and cavity length of 60 nm. A high value of sensitivity is achieved for each biomolecules when drain doping ranged from 1019 donors/cm3 to 5 × 1019 donors/cm3 and cavity length ranged between 40 nm to 50 nm. Effect of differently charged biomolecules on sensitivity has also be structured. [ABSTRACT FROM AUTHOR]

Armin Salek Maghsoudi,1,* Shokoufeh Hassani,1,2,* Milad Rezaei Akmal,3 Mohammad Reza Ganjali,3,4 Kayvan Mirnia,5 Parviz Norouzi,3,4 Mohammad Abdollahi1,2 1Department of Toxicology and Pharmacology, School of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran; 2Toxicology and Diseases Group (TDG), Pharmaceutical Sciences Research Center (PSRC), The Institute of Pharmaceutical Sciences (TIPS), Tehran University of Medical Sciences, Tehran, Iran; 3Center of Excellence in Electrochemistry, Faculty of Chemistry, University of Tehran, Tehran, Iran; 4Biosensor Research Center, Endocrinology and Metabolism Molecular-Cellular Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran; 5Department of Neonatology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran*These authors contributed equally to this workCorrespondence: Mohammad AbdollahiToxicology and Diseases Group (TDG), Pharmaceutical Sciences Research Center (PSRC), The Institute of Pharmaceutical Sciences (TIPS), Tehran University of Medical Sciences, Tehran 1417614411, IranTel +98 21 64122319Email mohammad@tums.ac.irPurpose: In the present study, a highly sensitive and simple electrochemical (EC) aptasensor for the detection of serpin A12 as a novel biomarker of diabetes was developed on a platform where flower-like gold microstructures (FLGMs) are electrodeposited onto a disposable screen-printed carbon electrode. Meanwhile, serpin A12-specific thiolated aptamer was covalently immobilized on the FLGMs.Methods: The electrochemical activity of a fabricated aptasensor under various conditions were examined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Aptamer concentration, deposition time, self-assembly time, and incubation time were optimized for assay of serpin A12. The differential pulse voltammetry (DPV) was implemented for quantitative detection of serpin A12 in K3 [Fe (CN) 6]/K4 [Fe (CN) 6] solution (redox probe).Results: The label-free aptasensor revealed a linear range of serpin A12 concentration (0.039– 10 ng/mL), detection limit of 0.020 ng/mL (S/N=3), and 0.031 ng/mL in solution buffer and plasma, respectively.Conclusion: The results indicate that this aptasensor has a high sensitivity, selectivity, stability, and acceptable reproducibility for detection of serpin A12 in diabetic patients.Keywords: electrochemical aptasensor, screen-printed carbon electrode, flower-like gold microstructures, label-free detection, serpin A12, diabetes biomarkers

This manuscript presents a comparative biosensing analysis of a dielectrically modulated dual-drain vertical TFET (DD-VTFET) by considering three distinct device arrangements based on the cavity position. DD-VTFETs with single cavity at the source and drain edge are called SC-DD-VTFET and DC-DD-VTFET, respectively, while for SDC-DD-VTFET, dual cavities are created at both the source and drain edge. Asymmetry in cavity position results in different electrostatics for each biosensor, leading to variation in their sensing performance. The on-current sensitivity is found to be lower for the DC-DD-VTFET due to the absence of cavity near the channel-source interface, while the SC-DD-VTFET shows poor performance in terms of ambipolar current sensitivity compared to the SDC-DD-VTFET. Moreover, the study includes the consideration of neutral and charged biomolecules (both positive and negative) with varying dielectric constants of 5, 7, 10 and 12. The sensitivity of partially filled nanogaps with fill-factor (FF) of 42% and 60%, influenced by steric hindrance, are also compared for all three DD-VTFET based biosensors which includes different step profiles of biomolecules, such as concave, convex, increasing, and decreasing. To consider the non-ideal state of the DD-VTFET based biosensors, the effect of irregular placement of the probe within the nano-cavity on different sensitivity parameters for a particular k -value of biomolecules is also analysed using TCAD simulator. Furthermore, the performance of the DD-VTFET based biosensor is quantitatively benchmarked against previously published works available in the literature. For a fully filled cavity with neutral biomolecules having dielectric constant of 12, SDC-DD-VTFET based label-free biosensor provides ON-current and current-switching ratio sensitivities approximately in the order of 10 5 , while the ambipolar current sensitivity of 2.1 × 10 3 is observed which makes the sensor equally suitable for sensing the biomolecules even at negative gate bias. • This paper investigates a dielectrically modulated DD-VTFET biosensor with different cavity positions. • SC-DD-VTFET biosensor with cavities on source and drain edges provides better sensitivity than devices with a single cavity. • The impact of charged biomolecules (both positive and negative) with varying k -value are also discussed in this work. • The study analyses DD-VTFET biosensors with variable fill-factors, assessing sensitivity under steric hindrance condition. • The effect of irregular probe placement within the nano-cavity on different sensitivity parameters is also analysed using TCAD simulator. [ABSTRACT FROM AUTHOR]

A split gated silicon nanotube field‐effect transistor (FET) biosensor has been proposed for the label free detection of the biomolecules for the first time in literature. The sensitivity of the sensing device has been analysed considering the on current (ION) and the threshold voltage (Vth) variation. Sub‐threshold regime has been considered here to detect the charged/neutral biomolecules. Extensive simulations have been done using the SILVACO ATLAS. Sensitivity analysis has been carried out by considering half‐filled and full‐filled nanogaps with the neutral or charged biomolecules inside the cavity. Significant sensitivity and excellent reduction in short‐channel effects has been observed in proposed biosensor. [ABSTRACT FROM AUTHOR]

A tapered single-mode coreless single-mode (SCS) structure with high sensitivity for sensing refractive index is described. In order to achieve high specificity of optical biosensors, here enzyme capsulation film was achieved by embedding urease in zeolitic imidazolate framework (ZIF-8/urease) through in situ growth approach on the coreless fibers. Determination of urea is achieved through online monitoring of its binding to the urease in zeolitic imidazolate framework. Refractive index change result in wavelength shifts of the optical fiber biosensor. The resonance wavelength exhibits a good linear relationship with urea concentration in the range of 1 to 10 mM with detection limit of 0.1 mM and sensitivity of 0.8 mM/RIU (refractive index unit) if operated with broadband light ranging from 1525 nm to 1590 nm. Final assessment of optical biosensor in real sample was performed where excellent performance in terms of sensitivity and selectivity was observed. [ABSTRACT FROM AUTHOR]

This research reports a portable immunochip, based on quartz crystal microbalance (QCM) for label-free, low-cost qualitative detection of zearalenone (ZEN) in food samples. The experimental parameters in the functionalization and working process were evaluated in detail, in order to achieve a high accuracy and sensitivity. Under optimal conditions, the ZEN concentration at an inhibition ratio of 50% and 15% of the proposed QCM immunochip achieved 3.41 µg L−1 and 0.37 µg L−1, respectively. This portable QCM immunochip also exhibited high specificity, no obvious cross-reaction to five structural analogs of ZEN, and showed other mycotoxins. It could finish the whole qualitative measurement within 30 min, showed good stability during the processes of preparation (SD < 5%, n = 9), storage (frequency response >90%, in PBS at 4 °C for 15 days), and application (frequency response >90% after being reused 6 times). The developed QCM immunochip obtained accurate and repeatable recovery results in ZEN analysis in the chosen food samples (corn, wheat flour, soy sauce, and milk), which had a high correlation (R2 = 0.9844) with that achieved by the HPLC–MS/MS method. In short, this work developed a portable, stable, and reproducible QCM immunochip that could be used for rapid, low-cost, and sensitively measurement of ZEN content in real food samples.

A rapid and quantitative method for the determination of N6-Benzylademine (N6-BA) was established through the application of surface-enhanced Raman spectroscopy (SERS). The Raman peak intensities of N6-BA at 1002 cm−1 positively correlated to N6-BA concentrations in sprout extracts. The R2 reached 0.99, and RSDs calculated below 10% at the concentration range of 0.1 ∼5μg mL−1. The average recoveries were 80.0% ∼ 98.2% for blank samples intentionally contaminated at differing levels of 0.04, 0.4, and 1 μg g−1. The whole procedure, including sample preparation and SERS detection, did not exceed 30 min for a set of 6 samples. This study indicates that SERS is a promising technique for rapid tracing analysis and on-site testing of N6-BA. [ABSTRACT FROM AUTHOR]

Microbial biofilm contamination is an ubiquitous and persistent problem in industry and clinics. The structure of the biofilm, its extracellular matrix and its formation process are very complex. At present, there are only limited options to investigate biofilms outside the lab, as most in situ techniques lack sensitivity and resolution. Impedance-based sensors provide a fast, label-free and sensitive manner to characterize biofilms, although mainly large electrodes have been used so far. Here, we used 60 μm-sized electrode arrays (MEAs) to characterize the structure of biofilms formed by wild type (WT) Escherichia coli TG1 and the isogenic ΔcsgD , ΔcsgB and ΔbcsA mutants. At 24 h of growth, the interfacial resistance at 2 Hz increased by 3.4% and 0.3% for the curli producing strains (WT and ΔbcsA ), yet it decreased by 5.7% and 4% for the curli non-producing strains ( ΔcsgD and ΔcsgB) . The imaginary impedance at 2 Hz decreased for all the strains by 7.2%, 6.9%, 5.1% and 2.5% (WT, ΔbcsA, ΔcsgB and ΔcsgD, respectively). Interestingly, the spatial variation of impedance within each biofilm, resulting from physiological and structural heterogeneity, was significantly different for each biofilm and most pronounced in the WT. Depending on the strain, the biofilm attachment phase lasted between 6 and 10 h, and was characterized by an increase in the interfacial resistance of up to 6% for the WT, 5.5% for ΔcsgD, 3.5% for ΔcsgB and 5% for ΔbcsA, as opposed to the decrease in medium resistance observed during the maturation phase. Overall, impedance-based MEA assays proved effective to differentiate between biofilms with varying structure, detect spatial diversity and explain biofilm life-cycle in terms of attachment and maturation. [ABSTRACT FROM AUTHOR]

In this paper the field-effect transistor DNA biosensor for detecting hepatitis B virus (HBV) based on indium tin oxide nanowires (ITO NWs) in label free approach has been fabricated. Because of ITO nanowires intensive conductance and functional modified surface, the probe immobilization and target hybridization were increased strongly. The high resolution transmission electron microscopy (HRTEM) measurement showed that ITO nanowires were crystalline and less than 50 nm in diameter. The single-stranded hepatitis B virus DNA (SS-DNA) was immobilized as probe on the Au-modified nanowires. The DNA targets were measured in a linear concentration range from 1fM to 10 µM. The detection limit of the DNA biosensor was about 1fM. The time of the hybridization process for defined single strand was 90 min. The switching ratio of the biosensor between "on" and "off" state was ~ 1.1 × 10 5 . For sensing the specificity of the biosensor, non-complementary, mismatch and complementary DNA oligonucleotide sequences were clearly discriminated. The HBV biosensor confirmed the highly satisfied specificity for differentiating complementary sequences from non-complementary and the mismatch oligonucleotides. The response time of the DNA sensor was 37 s with a high reproducibility. The stability and repeatability of the DNA biosensor showed that the peak current of the biosensor retained 98% and 96% of its initial response for measurements after three and five weeks, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • 2,5-bis(4-hydroxyphenyl)thiazolo[5,4- d ]thiazole fluorophore was used to prepare in-situ cross-linked nanofiber that enables reductant-free, green synthesis of AgNPs on the surface. • AgNPs decorated PVA nanofibers was successfully prepared and used as SERS substrate. • AgNPs decorated PVA nanofibers SERS substrate was successfully applied to the ultra-sensitive detection of organic pollutants. • R6G and pNP molecules could be detected up to 10−13 M using AgNPs decorated PVA nanofibers SERS substrate. Detection and particularly quantitative analysis of organic pollutants such as rhodamine 6G (R6G), and p-nitrophenol (pNP) in water are very important for both human health and the ecological environment. In this study, we synthesized as a facile and low cost method silver nanoparticles on poly(vinyl alcohol) (PVA) nanofibers to prepare a film based surface enhancement Raman scattering (SERS) substrate for label free molecular detection. Detection of the R6G molecule with the obtained SERS substrate is possible even at concentrations as low as 10−12 M and therefore the obtained SERS substrate indicated excellent molecular sensitivity for R6G molecule. Limit of detection value (LOD) was determined as 1.07 × 10−13 M while the enhancement factor (EF) of the obtained SERS substrate was calculated as 1.06 × 109 for the R6G molecule. A fluorophore molecule named as 2,5-bis(4-hydroxyphenyl)thiazolo[5,4- d ]thiazole (HPhTT) was effectively used for cross-linking of PVA nanofibers to use them as growth template for silver nanoparticles (AgNPs) formation on the surface without any reducing and stabilizing agent thanks to unique properties of HPhTT. Green and one pot preparation of such SERS substrates can pave the way for easily prepared commercial substrates. Moreover, AgNPs decorated PVA nanofiber-based SERS substrate has high reproducibility and good stability for SERS detection of organic pollutants. Obtained SERS substrate is expected to be applicable as a label-free sensor for various chemical and biological molecules. [ABSTRACT FROM AUTHOR]

The authors describe a lysozyme aptasensor based on the use of gold nanoparticles (AuNP) assembled on the carbon nanotubes, graphene oxide and chitosan. An electrochemical impedance spectroscopic study was performed to demonstrate the synergistic effect of the MWCNT-AuNP, Chit-AuNP and GO-AuNP composites and the order of the layers affect the performance of aptasensing. Different parameters were optimized in order to obtain successful and sensitive detection of lysozyme in urine and saliva samples. A plot of charge-transfer resistance versus the logarithm of the lysozyme concentration is linear in the 0.02 to 250 pM concentration range, with a 9 fM detection limit (at an S/N ratio of 3). The aptasensor is highly specific and selective. Clinical analyses were performed and data were found to be in good agreement with those obtained by HPLC. [ABSTRACT FROM AUTHOR]

The detection and targeting of both the mismatched and abasic DNA is highly important which would ultimately help in designing new diagnostics and chemotherapeutics. Furthermore, sensing and targeting the bulge sequence with a fluorescent probe would be useful to study the role of bulges in nucleic acid function or could have significant therapeutic potential. Thus, detection of specific bulges by small fluorescent molecules is an attractive research area since the past several years. Many attempts have been made to prepare such compounds. We report herein a label free strategy for the detection of pyrimidine base mismatches (T/T and C/C), sensing of abasic site, and pyrimidine base bulge DNA using an unnatural tetrazolylpyrene nucleoside ( TPy B Do ) as a bare fluorescent probe. The H-bonding/hydrophobic force mediated interactions allow the sensing of all three deformed DNA via an enhancement of fluorescence signal using our simple “Just-Mix and Read” strategy. The binding of the probe to all the three deformed DNA duplexes is accompanied by an increase in the thermal melting stability of the deformed DNAs. That the probe binds efficiently to the minor groove near the deformed site was evident from spectroscopic studies. All the spectral evidences open up a multitude of possibilities for using our probe, tetrazolylpyrene nucleoside, as an efficient fluorescent light-up bio-probe for label free DNA detection. [ABSTRACT FROM AUTHOR]

A densely packed gold nanoparticles on the rGO-MWCNT platform was used as the basis for an ultrasensitive label-free electrochemical aptasensor to detect the biomarker prostate specific antigen (PSA) in serum. The detection was based on that the variation of electron transfer resistance (R ct ) and differential pulse voltammetry (DPV) current were relevant to the formation of PSA–aptamer complex at the modified electrode surface. Compared with pure AuNPs, rGO-MWCNT and MWCNT/AuNPs, the rGO-MWCNT/AuNPs nanocomposite modified electrode was the most sensitive aptasensing platform for the determination of PSA. Two calibration curves were prepared from the data obtained from the DPV and electrochemical impedance spectroscopy (EIS) by plotting the peak current and R ct against PSA concentration, respectively. The proposed aptasensor had an extremely low LOD of 1.0 pg mL −1 PSA within the detection range of 0.005–20 ng mL −1 and 0.005–100 ng mL −1 for DPV and EIS calibration curves, respectively. This sensor exhibited outstanding anti-interference ability towards co-existing molecules with good stability, sensitivity, and reproducibility. Clinical application was performed with analysis of the PSA levels in serum samples obtained from patients with prostate cancer using both the aptasensor and Immunoradiometric assay. The results revealed the proposed system to be a promising candidate for clinical analysis of PSA. [ABSTRACT FROM AUTHOR]

A feasibility study for a label-free, multi-marker single sensor using electrochemical impedance spectroscopy (EIS), imaginary impedance, and a signal decoupling technique is reported. To our knowledge, this is the first reported attempt of using imaginary impedance for biomarker detection and multi-marker detection. The electrochemical responses of purified low and high density lipoproteins (LDL and HDL, respectively) were first individually characterized through the immobilization of their molecular recognition elements (MREs) onto gold disk electrodes (GDEs). The co-immobilization was performed by immobilizing the MREs of both LDL and HDL on the same GDE, which was then used to detect LDL and HDL simultaneously in mixed solution. Previous individual purified responses were then used to de-convolute the mixed response, when the two biomarkers were detected in mixed solutions. The optimal frequencies of LDL and HDL were found to be 81.38 Hz and 5.49 Hz, respectively, which shifted to 175.8 Hz and 3.74 Hz under co-immobilized conditions. After comparing the electrochemical signal in complex and imaginary impedance, imaginary impedance was found to be more suitable for multi-marker detection purposes. Since imaginary impedance is related to capacitance, electric displacement, relative permittivity, and effective capacitance were derived to elucidate the theory of optimal frequency. This work shows that EIS has the potential for multi-marker detection and can be extended to monitor other complex diseases such as diabetes mellitus for better management and diagnostic purposes. [ABSTRACT FROM AUTHOR]

Various methodologies have been reported in the literature for the qualitative and quantitative monitoring of mycotoxins in food and feed samples. Based on their enhanced specificity, selectivity and versatility, bio-affinity assays have inspired many researchers to develop sensors by exploring bio-recognition phenomena. However, a significant problem in the fabrication of these devices is that most of the biomolecules do not generate an easily measurable signal upon binding to the target analytes, and signal-generating labels are required to perform the measurements. In this context, aptamers have been emerged as a potential and attractive bio-recognition element to design label-free aptasensors for various target analytes. Contrary to other bioreceptor-based approaches, the aptamer-based assays rely on antigen binding-induced conformational changes or oligomerization states rather than binding-assisted changes in adsorbed mass or charge. This review will focus on current designs in label-free conformational switchable design strategies, with a particular focus on applications in the detection of mycotoxins. [ABSTRACT FROM AUTHOR]

A sensitive aptasensor based on a robust nanocomposite of titanium dioxide nanoparticles, multiwalled carbon nanotubes (MWCNT), chitosan and a novel synthesized Schiff base (SB) (TiO 2 /MWCNT/CHIT/SB) on the surface of a glassy carbon electrode (GCE) was developed for thrombin detection. The resultant nanocomposite can provide a large surface area, excellent electrocatalytic activity, and high stability, which would improve immobilization sites for biological molecules, allow remarkable amplification of the electrochemical signal and contribute to improved sensitivity. Thrombin aptamers were simply immobilized onto the TiO 2 -MWCNT/CHIT-SB nanocomposite matrix through simple π - π stacking and electrostatic interactions between CHIT/SB and aptamer strands. The electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to analyze the surface characterization of unmodified GCE and TiO 2 -MWCNT/CHIT-SB modified GCE, and also the interaction between aptamer and thrombin. In the presence of thrombin, the aptamer on the adsorbent layer captures the target on the electrode interface, which makes a barrier for electrons and inhibits electron transfer, thereby resulting in decreased DPV and increased impedance signals of the TiO 2 -MWCNT/CHIT-SB modified GCE. Furthermore, the proposed aptasensor has a very low LOD of 1.0 fmol L −1 thrombin within the detection range of 0.00005–10 nmol L −1 . The aptasensor also presents high specificity and reproducibility for thrombin, which is unaffected by the coexistence of other proteins. Clinical application was performed with analysis of the thrombin levels in blood and CSF samples obtained from patients with MS, Parkinson, Epilepsy and Polyneuropathy using both the aptasensor and commercial ELISA kit. The results revealed the proposed system to be a promising candidate for clinical analysis of thrombin. [ABSTRACT FROM AUTHOR]

This review presents an overview of 'Lab on Fiber' technologies and devices with special focus on the design and development of advanced fiber optic nanoprobes for biological applications. Depending on the specific location where functional materials at micro and nanoscale are integrated, 'Lab on Fiber Technology' is classified into three main paradigms: Lab on Tip (where functional materials are integrated onto the optical fiber tip), Lab around Fiber (where functional materials are integrated on the outer surface of optical fibers), and Lab in Fiber (where functional materials are integrated within the holey structure of specialty optical fibers). This work reviews the strategies, the main achievements and related devices developed in the 'Lab on Fiber' roadmap, discussing perspectives and challenges that lie ahead, with special focus on biological sensing applications. [ABSTRACT FROM AUTHOR]

Aflatoxin B1 (AFB1) is the most prevalent and toxic contaminant for human beings and animals among all the aflatoxins (AFs). Additionally, AFB1 is documented as a highly carcinogenic and mutagenic contaminant in the literature. Therefore, it is of vital importance to monitor AFB1 contamination to reduce its health associated risks. In the present work, we have designed a label-free electrochemical impedimetric aptasensor for aflatoxin B1 detection. Herein, we compared the analytical performances of two aptamer sequences (seqA and seqB). The detection is based on specific recognition by the aptamer covalently-bound as compact monolayer on screen printed carbon electrodes (SPCEs) via diazonium coupling reaction. The quantification of AFB1 was achieved by using electrochemical impedance spectroscopy. A dynamic quantification range from 0.125 ng mL −1 to 16 ng mL −1 was obtained with both types of aptamer sequences while the detection limits were 0.12 ng mL −1 and 0.25 ng mL −1 for seqA and seqB respectively. For real sample applications, the developed aptasensors were demonstrated in beer and wine samples, and good recovery levels in the range of 92–102% were recorded for AFB1 detection. [ABSTRACT FROM AUTHOR]

This work presents a comparison of two different aptamers (Apts) (COX and TRAN) for the detection of a ubiquitous protein Lysozyme (Lys) using Apt-based biosensors. The detection is based on the specific recognition by the Apt immobilized on screen printed carbon electrodes (SPCEs) via diazonium coupling reaction. The quantitative detection of Lys protein was achieved by electrochemical impedance spectroscopy (EIS). A very good linearity and detection limits for the quantitation of Lys were obtained from 0.1 to 0.8 μM and 100 nM using Apt COX and from 0.025 to 0.8 μM and 25 nM using Apt TRAN respectively. The obtained results showed that the developed aptasensors exhibit good specificity, stability and reproducibility for Lys detection. For real application, the aptasensors were tested in wine samples and good recovery rates were recorded in the range from 94.2 to 102% for Lys detection. The obtained recovery rates confirm the reliability and suitability of the developed method in wine matrix. The developed method could be a useful and promising platform for detection of Lys in different applications. [ABSTRACT FROM AUTHOR]

Nanoporous SnO2 thin films were elaborated to serve as sensing electrodes for label-free DNA detection using electrochemical impedance spectroscopy (EIS). Films were deposited by an electrodeposition process (EDP). Then the non-Faradic EIS behaviour was thoroughly investigated during some different steps of functionalization up to DNA hybridization. The results have shown a systematic decrease of the impedance upon DNA hybridization. The impedance decrease is attributed to an enhanced penetration of ionic species within the film volume. Besides, the comparison of impedance variations upon DNA hybridization between the liquid and vapour phase processes for organosilane (APTES) grafting on the nanoporous SnO2 films showed that vapour-phase method is more efficient. This is due to the fact that the vapour is more effective than the solution in penetrating the nanopores of the films. As a result, the DNA sensors built from vapour-treated silane layer exhibit a higher sensitivity than those produced from liquid-treated silane, in the range of tested target DNA concentration going to 10 nM. Finally, the impedance and fluorescence response signals strongly depend on the types of target DNA molecules, demonstrating a high selectivity of the process on nanoporous SnO2 films. [ABSTRACT FROM AUTHOR]

Förster resonance energy transfer (FRET) occurs when the distance between a donor fluorophore and an acceptor is within 10 nm, and its application often necessitates fluorescent labeling of biological targets. However, covalent modification of biomolecules can inadvertently give rise to conformational and/or functional changes. This review describes the application of intrinsic protein fluorescence, predominantly derived from tryptophan (λEX ~ 280 nm, λEM ~ 350 nm), in protein-related research and mainly focuses on label-free FRET techniques. In terms of wavelength and intensity, tryptophan fluorescence is strongly influenced by its (or the protein's) local environment, which, in addition to fluorescence quenching, has been applied to study protein conformational changes. Intrinsic Förster resonance energy transfer (iFRET), a recently developed technique, utilizes the intrinsic fluorescence of tryptophan in conjunction with target-specific fluorescent probes as FRET donors and acceptors, respectively, for real time detection of native proteins. [ABSTRACT FROM AUTHOR]

Highlights: [•] K+ image sensor was developed using a PVC membrane coated on a 128×128pixels CCD pH image sensor. [•] The sensitivity was 50mV/decade for a K+ concentration of 10−3 to 10−1 M. [•] Glutamate-induced changes in the K+ were recorded in the hippocampal slices. [•] The imaging of K+ release from hippocampal neurons was demonstrated without labeling. [ABSTRACT FROM AUTHOR]

Abstract: Blood safety is a global health goal. In developed countries, bacterial contamination of platelet concentrates is the highest infectious risk in transfusion despite the current preventive strategies. We aimed to develop a conductometric biosensor for the generic, rapid and sensitive detection of Gram-negative bacteria. Our strategy is based on immunosensors: addressable magnetic nanoparticles coupled with anti-LPS antibodies were used for the generic capture of Gram-negative bacteria. Bacterial capture was characterized by impedancemetric and microscopic measurements. The results obtained with conductometric measurements allowed real-time, sensitive detection of Escherichia coli or Serratia marcescens cultures from 1 to 103 CFUmL−1. The ability of the immunosensor to detect Gram negative bacteria was also tested on clinically relevant strains. The conductometric immunosensor allowed the direct detection of 10–103 CFUmL−1 of Pseudomonas aeruginosa and Acinetobacter baumannii strains that were undetectable using standard immunoblot methods. Results showed that the conductometric response was not inhibited in 1% serum. [Copyright &y& Elsevier]

Abstract: A high-density electrical-impedance spectroscopy (EIS) biosensor array has been developed for high-throughput and automated counting of specific breast tumor MCF-7 cells. The biosensor array (96×96) consists of densely packed electrodes. Each of the square electrodes has an edge-length of 22μm to capture single MCF-7 cell. The electrodes are electrically addressable by decoding circuit built underneath by 0.18μm CMOS process. EIS spectra of electrodes were recorded over a wide frequency range with and without the presence of cell. Data were numerically fitted with the equivalent circuit model to extract important sensing parameters including cell impedance, electrode impedance, sealing resistance and spreading resistance. Results revealed a distinctive impedance increase from 50kHz to 500kHz, where the maximum (∼21% increment) occurs at 200kHz. Enumeration of circulating tumor cells (CTCs) was performed by scanning an interrogation area of hundred electrodes at the optimum frequency. The developed EIS platform has demonstrated the electrical impedance detection with single cell resolution and enumeration with mapping accuracy of ∼90%. [Copyright &y& Elsevier]

Surface-enhanced Raman scattering (SERS) takes advantage of the giant electromagnetic field enhancement provided by localized surface plasmons in metal nanoparticles to amplify the weak Raman scattering of the molecules. Optical fibers coated with noble metal nanoparticles can therefore be used as SERS-based sensors for remote detection of molecular species. In this article, we report on the development of an optical fiber SERS sensor capable to operate on a range of excitation wavelengths from the visible to the near-infrared. We introduce a quasistatic chemical etching protocol to engineer the tip shape and investigate the effects of the tip shape on the sensor performances. [ABSTRACT FROM AUTHOR]

Abstract: We present a high-throughput label-free electrical-impedance spectroscopy (EIS) platform composed of a 96×96 microelectrode array for counting and analysis of breast tumor cells (MCF-7). These Au-electrodes are densely packed within a 3.5mm×3.5mm interrogation region. Each Au-electrode has an edge-length of 25μm designed to detect single tumor cell by electrical impedance spectroscopy. The detected signal is read out via an integrated circuit (IC) of addressable electrode-selection-switch array manufactured with 0.18μm CMOS technology. The independently addressable microelectrode array is integrated onto a printed circuit board (PCB) containing associated circuitry for electrode switching and readout. MCF-7 cells were dispensed onto the chip surface and EIS measurements were recorded before and after the cell dispensation. On an average 20% increase in impedance was found associated with cell occupancy on the electrode surface. A positive correlation was observed between cell detection with optical microscopy and with electrical scanning. [Copyright &y& Elsevier]

Abstract: A method for label-free, electrochemical impedance immunosensing for the detection and quantification of three infection biomarkers in both buffer and directly in the defined model matrix of mock wound fluid is demonstrated. Triggering Receptor-1 Expressed on Myeloid cells (TREM-1) and Matrix MetalloPeptidase 9 (MMP-9) are detected via direct assay and N-3-oxo-dodecanoyl-l-HomoSerineLactone (HSL), relevant in bacterial quorum sensing, is detected using a competition assay. Detection is performed with gold screen-printed electrodes modified with a specific thiolated antibody. Detection is achieved in less than 1h straight from mock wound fluid without any extensive sample preparation steps. The limits of detection of 3.3pM for TREM-1, 1.1nM for MMP-9 and 1.4nM for HSL are either near or below the threshold required to indicate infection. A relatively large dynamic range for sensor response is also found, consistent with interaction between neighbouring antibody–antigen complexes in the close-packed surface layer. Together, these three novel electrochemical immunosensors demonstrate viable multi-parameter sensing with the required sensitivity for rapid wound infection detection directly from a clinically relevant specimen. [Copyright &y& Elsevier]

Abstract: This paper describes a label free and fully electronic 32×32 CMOS DNA image sensor fabricated in a 1-poly 1-metal CMOS technology, suitable for inexpensive and highly integrated applications. The pixel operates using the charge transfer technique. DNA immobilization and hybridization on the silane-coated surface are detected, as well as variations in the silane coating. Significant output voltages of 76.4±16.5mV and 64.5±15.7mV were measured after immobilization and hybridization of DNA molecules containing 22 bases. From these results, the immobilized and hybridized DNA densities were estimated. These were 6.3±1.4×108 cm−2 and 5.3±1.3×108 cm−2, respectively. The DNA detection limit was calculated to be approximately 2.7×107 cm−2 molecules (22 bases). Thanks to its potentiometric detectability, the DNA immobilization and hybridization was successfully verified. [Copyright &y& Elsevier]

Abstract: This paper investigates a new immobilization procedure for biological molecules that is based on the formation of reactive ω-functionalized-self-assembled thiol monolayers onto a gold electrode. The homogeneous self-assembled monolayer was characterized by X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The SAM modified gold electrode showed a clear peak corresponding to S2p that characterized the Au-thiolate bond, while cyclic voltammetry and electrochemical impedance spectroscopy measurements, in 10 mM phosphate buffer pH 7, in the presence of Fe(CN)6 −3/−4 as redox probe, showed that these monolayers were densely packed and prevented electron transfer towards the gold surface. These homogeneous SAMs were used to immobilize biotin hydrazide by covalent attachment, after the nucleophilic attack of the amino group of biotin hydrazide on the ω-activated ester function of thiols. The biotin–avidin interaction was then examined as a model for an affinity biosensor with electrochemical impedance spectroscopy. A Randles equivalent circuit was used for the interpretation of impedance data and the change in the interfacial properties at the modified-electrode/electrolyte interface were monitored through charge-transfer resistance variation. The proposed affinity biosensor showed a detection range that was linear between 200 and 800 ng/ml for avidin. In order to improve the sensitivity the technique of mixed self-assembled monolayers was adopted. Mixed SAMs were elaborated by co-adsorption of two differently substituted thiols, one was substituted by a reactive group that was used to react with the amino group of biotin hydrazide, whereas the other was substituted by an hydroxyl group that was chosen to mimic protein resistance. In this study, we started with a 1:3 activated ester:hydroxyl-terminated alkanethiol ratio. The results obtained with the mixed SAMs appeared to be better than those obtained with the homogeneous SAMs, and the corresponding affinity biosensor presented two detection ranges that were linear between 20 and 100 ng/ml and between 100 and 1200 ng/ml, respectively, with two different slopes. [Copyright &y& Elsevier]

Abstract: We demonstrated a novel application of transient coulostatic pulse technique for the detection of label free DNA hybridization on nm-sized gold interdigitated ultramicroelectrode arrays (Au–IDA) made in silicon technology. The array consists of eight different positions with an Au–IDA pair at each position arranged on the Si-based Biochip. Immobilization of capture probes onto the Au–IDA was accomplished by self-assembling of thiol-modified oligonucleotides. Target hybridization was indicated by a change in the magnitude of the time dependant potential relaxation curve in presence of electroactive Fe(CN)6 3− in the phosphate buffer solution. While complementary DNA hybridization showed 50% increase in the relaxation potential, the non-complementary DNA showed a negligible change. A constant behaviour was noted for all positions. The dsDNA specific intercalating molecule, methylene blue, was found to be enhancing the discrimination effect. The changes in the relaxation potential curves were further corroborated following the ELISA like experiments using ExtraAvidine alkaline phosphatase labelling and redox recycling of para-aminophenol phosphate at IDAs. The coulostatic pulse technique was shown to be useful for identifying DNA sequences from brain tumour gene CK20, human herpes simplex virus, cytomegalovirus, Epstein–Barr virus and M13 phage. Compared to the hybridization of short chain ONTs (27mers), the hybridization of long chain M13 phage DNA showed three times higher increase in the relaxation curves. The method is fast enough to monitor hybridization interactions in milli or microsecond time scales and is well suitable for miniaturization and integration compared to the common impedance techniques for developing capacitative DNA sensors. [Copyright &y& Elsevier]

Charge sensitive optical detection (CSOD) technique is a label-free method for real-time measurement of molecular interactions. Traditional label-free optical detection techniques mostly measure the mass of a molecule, and they are less sensitive to small molecules. In contrast, CSOD detects the charge of a molecule, where the signal does not diminish with the size of the molecule, thus capable for studying small molecules. In addition, CSOD is compatible with the standard microplate platform, making it suitable for high-throughput screening of drug candidates. In CSOD, an optical fiber functionalized with the probe molecule is dipped into a well of a microplate where an alternate perpendicular electrical field is applied to the fiber, which drives the fiber into oscillation because of the presence of surface charge on the fiber. The binding of the target molecules changes the charge of the fiber, and thus the amplitude and phase of the oscillating fiber, which are precisely measured through tracking of the optical images of the fiber tip., (© 2022. Springer Science+Business Media, LLC, part of Springer Nature.)

This research reports a portable immunochip, based on quartz crystal microbalance (QCM) for label-free, low-cost qualitative detection of zearalenone (ZEN) in food samples. The experimental parameters in the functionalization and working process were evaluated in detail, in order to achieve a high accuracy and sensitivity. Under optimal conditions, the ZEN concentration at an inhibition ratio of 50% and 15% of the proposed QCM immunochip achieved 3.41 µg L−1 and 0.37 µg L−1, respectively. This portable QCM immunochip also exhibited high specificity, no obvious cross-reaction to five structural analogs of ZEN, and showed other mycotoxins. It could finish the whole qualitative measurement within 30 min, showed good stability during the processes of preparation (SD < 5%, n = 9), storage (frequency response >90%, in PBS at 4 °C for 15 days), and application (frequency response >90% after being reused 6 times). The developed QCM immunochip obtained accurate and repeatable recovery results in ZEN analysis in the chosen food samples (corn, wheat flour, soy sauce, and milk), which had a high correlation (R2 = 0.9844) with that achieved by the HPLC–MS/MS method. In short, this work developed a portable, stable, and reproducible QCM immunochip that could be used for rapid, low-cost, and sensitively measurement of ZEN content in real food samples. [ABSTRACT FROM AUTHOR]

• AuNPs aggregate in the presence of cationic polymer. • Freely dispersed AuNPs resists free electrons to reach electrode surface. • Aptamer specifically bind to its target for complex formation. • Change in electrostatic interactions can be observed by change in current. To date, NS1 viral diagnostic technologies have been considered as time-consuming, expensive and too complex to be widely deployed, particularly in developing countries. In view of this, an electrochemical method was exploited to detect dengue virus based on NS1-specific aptamer and cationic polymer-induced aggregation of gold nanoparticles (AuNPs). The basic principle of this assay is classical based on the gradual aggregation of AuNPs controlled by the specific interactions among polyethyleneimine (PEI), aptamer and NS1. The aggregation of AuNPs was induced by the cationic polymer, which was controlled by the interaction of aptamer and cationic polymer forming "duplex" structure. This non-specific interaction between aptamer and polymer was expected to limit the flexibility of the aptameric chain and consequently renders the aptamer to be more accessible to the target molecule (NS1). This accession of NS1 was responsible for the quadruplexe formation due to strong obligatory electrostatic interaction with aptamer. This structural switching between aptamer/polymer duplex and aptamer/target complex was the base to design this electrochemical aptasensor. This cationic polymer and aptamer assisted dispersion-aggregation phenomenon renders change in their electrochemical response which could eventually probe the sensitive detection of NS1 protein. The as prepared electrochemical aptasensor successfully detected NS-1 protein with enhanced limit of detection (0.3 ng mL−1) and linear range (3–160 ng mL−1). Human real serum analysis indicated the actual applicability of our E-Apts. Using this electrochemical aptasensor, we demonstrate the highly sensitive and specific detection of Dengue virus. The low-cost and flexibility inherent in this analytical technique could be an important step towards effective diagnostic technology for the detection of Dengue virus and other infectious diseases. [ABSTRACT FROM AUTHOR]

Incredible progress continues to be made toward development of low-cost nucleic acid-based diagnostic solutions suitable for deployment in resource-limited settings. Detection components play a vitally important role in these systems, but have proven challenging to adapt for operation in a portable format. Here we describe efforts aimed at leveraging the capabilities of consumer-class smartphones as a convenient platform to enable detection of nucleic acid products associated with DNA amplification via the polymerase chain reaction (PCR). First, we show how fluorescence-based detection can be incorporated into a portable convective thermocycling system controlled by a smartphone app. Raw images captured by the phone's camera are processed to yield real-time amplification data comparable to benchtop instruments. Next, we leverage smartphone imaging to achieve label-free detection of PCR products by monitoring changes in electrochemical reactivity of embedded metal electrodes as the target DNA concentration increases during replication. These advancements make it possible to construct rugged inexpensive nucleic acid detection components that can be readily embedded in a variety of portable bioanalysis instruments.