A novel aptasensor platform for the detection of carcinoembryonic antigen using quartz crystal microbalance.

In this study, a quartz crystal microbalance (QCM) aptasensor for carcinoembryonic antigen (CEA), a well-known biomarker for various cancer types, was reported, utilizing two different aptamers. To achieve this, a nanofilm of 4-mercaptophenyl was electrochemically attached to gold-coated QCM crystal surfaces via the reduction of 4-mercaptobenzenediazonium salt (4 MB-DAT) using cyclic voltammetry. Subsequently, gold nanoparticles (AuNP) were affixed to this structure, and then aptamers (antiCEA1 and antiCEA2) modified with SH-functional ends bound to AuNPs completed the modification. The analytical performance of the CEA sensor was evaluated through simultaneous QCM measurements employing CEA solutions ranging from 0.1 ng/mL to 25 ng/mL. The detection limit (LOD) for CEA was determined to be 102 pg/mL for antiCEA1 and 108 pg/mL for antiCEA2 aptamers. Interday and intraday precision and accuracy tests yielded maximum results of 4.3 and + 3.8, respectively, for both aptasensors, as measured by relative standard deviation (RSD%) and relative error (RE%). The kinetic data of the aptasensors resulted in affinity values (KD) of 0.43 ± 0.14 nM for antiCEA1 and 0.75 ± 0.42 nM for antiCEA2. These values were lower than the reported values of 3.9 nM and 37.8 nM for both aptamers, respectively. The selectivity of the aptasensor was evaluated by measuring the signal changes caused by alpha-fetoprotein (AFP), cancer antigen (CA-125), and vascular endothelial growth factor (VEGF-165) individually and together at a concentration of 500 ng/mL, resulting in a maximum 4.1 % change, which was comparable to precision and accuracy values reported in the literature. After confirming the selectivity of the aptamers, recovery experiments were conducted using spiked commercial serum samples to simulate real samples, and the lowest recovery value obtained was 95.4 %. It was determined that two different aptasensors could be successfully used for the QCM-based detection of CEA in this study.

Structural switching aptamer-based electrochemical sensor for mycotoxin patulin detection.

In this study, an electrochemical and aptamer-based aptasensor was developed for the sensitive detection of patulin, a mycotoxin commonly found in fruits and fruit-based products. The aptasensor used an innovative structural switching signal-off platform for detecting patulin. The aptamer immobilization on screen-printed carbon electrodes was achieved through Au electrodeposition and thiol group (-SH) route. Response surface methodology was used to determine the optimal incubation times for the aptamer, blocking agent, and target molecule, which were found to be 180 min, 40 min, and 89 min, respectively. The response of the aptamer to different concentrations of patulin was measured using square wave voltammetry by exploiting the structural switching mechanism. The sensor response was determined by quantifying differences in the aptasensor's background current. The aptasensor exhibited a linear working range of 1-25 µM and a low detection limit of 3.56 ng/mL for patulin. The aptasensor's relative standard deviation and accuracy were determined to be 0.067 and 94.4%, respectively. A non-specific interaction was observed at low concentrations of two other mycotoxins, ochratoxin A and zearalenone. The interference from ochratoxin A in the measurements was below 10%. In real sample tests using apple juice, interference, particularly at low concentrations, had changed the recovery of patulin negatively with a significant effect on the structural switching behavior. Nevertheless, at a concentration of 25 ng/mL, the interference effect was eliminated, and the recovery standard deviation improved to 6.6%. The aptasensor's stability was evaluated over 10 days, and it demonstrated good performance, retaining 13.12% of its initial response. These findings demonstrate the potential of the developed electrochemical aptasensor for the sensitive detection of patulin in fruit-based products, with prospects for application in food safety and quality control.

An Overview of Biosensors for the Detection of Patulin Focusing on Aptamer-Based Strategies.

Patulin is a low molecular weight mycotoxin and poses a global problem, especially threatening food safety. It is also resistant to processing temperatures and is commonly found in fruits and vegetables. Studies have shown that it has toxic effects on animals and humans and the severity of patulin toxicity depends on the amount ingested. Therefore, the consumption of contaminated products, especially in infants and children, is important. The maximum daily intake of PAT that can be tolerated is found to be 0.4 µg/kg body weight to prevent chronic effects and the maximum residue limits in food samples were given as 50 ng/g (∼320 nM). Conventional methods for the detection of PAT have many disadvantages such as the use of expensive equipment, the need for trained personnel, and complicated sample preparation steps. To this extent, various numbers of research have been conducted on selective and sensitive detection of patulin using biosensor platforms in various media. This review presents an overview of the current literature dealing with the studies to develop patulin-specific aptamer-based biosensors and adapts various immobilization methods to increase the sensor response using different nanomaterials. Furthermore, a comparison of biosensors with conventional methods is presented using analytical performance parameters and their practicality for the detection of patulin.

An Overview of Aptamer-Based Sensor Platforms for the Detection of Bisphenol-A.

Endocrine disruptive compounds are natural or anthropogenic environmental micropollutants that alter the function of the endocrine system ultimately damaging the metabolism. Bisphenol A (BPA) is the most common of these pollutants and it is often used in epoxy coatings and polycarbonates as a plasticizer. Therefore, monitoring BPA levels in different environments is very important and challenging. In recent years, an increasing number of BPA detection methods have been proposed. This article presents a critical review of aptamer-based electrochemical, fluorescence-based, colorimetric, and several other BPA detection platforms published in the last decade. Furthermore, a statistical evaluation has been made using principle component analysis showing analytical performance parameters do not create very different clusters. Comparisons to other BPA detection methods are also presented so that the reader has an overall literature overview.

Mechanical test and friction-mapping on recycled polypropylene beads using atomic force microscopy.

Mechanical tests at sub-micron scales using force microscopy are often used for the characterization of materials. Here we report the mechanical, tribologic, and morphological characterization of recycled polypropylene beads using force spectroscopy and lateral-force microscopy. The compression-elastic moduli calculated using the Hertzian model for polypropylene beads was between 0.448 ± 0.010 and 1.044 ± 0.057 GPa. The grain size analysis revealed a significant correlation between the grain size and measured compression-elastic moduli. Friction-maps of recycled polypropylene beads obtained using lateral-force microscopy were also reported for 25 µm2 scanning areas.

Sensor and Bioimaging Studies Based on Carbon Quantum Dots: The Green Chemistry Approach.

Since carbon quantum dots have high photoluminescent efficiency, it has been a desired material in sensor and bioimaging applications. In recent years, the green chemistry approach has been preferred and the production of quantum dots has been reported in many studies using different precursors from natural, abundant, or waste sources. Hydrothermal, chemical oxidation, microwave supported, ultrasonic, solvothermal, pyrolysis, laser etching, solid-state, plasma, and electrochemical methods have been reported in the literature. In this review article, green chemistry strategies for carbon quantum dot synthesis is summarized and compared with conventional methods using methodologic and statistical data. Furthermore, a detailed discussion on sensor and bioimaging applications of carbon quantum dots produced with green synthesis approaches are presented with a special focus on the last decade.

Detection Strategies of Zearalenone for Food Safety: A Review.

Zearalenone (ZEN) is a toxic compound produced by the metabolism of fungi (genus Fusarium) that threaten the food and agricultural industry belonging to the in foods and feeds. ZEN has toxic effects on human and animal health due to its mutagenicity, teratogenicity, carcinogenicity, nephrotoxicity, immunotoxicity, and genotoxicity. To ensure food safety, rapid, precise, and reliable analytical methods can be developed for the detection of toxins such as ZEN. Different selective molecular diagnostic elements are used in conjunction with different detection strategies to achieve this goal. In this review, the use of electrochemical, colorimetric, fluorometric, refractometric as well as other strategies were discussed for ZEN detection. The success of the sensors in analytical performance depends on the development of receptors with increased affinity to the target. This requirement has been met with different immunoassays, aptamer-assays, and molecular imprinting techniques. The immobilization techniques and analysis strategies developed with the combination of nanomaterials provided high precision, reliability, and convenience in ZEN detection, in which electrochemical strategies perform the best.

Spectroscopic ellipsometry methods for brevetoxin detection.

The spectroscopic ellipsometry (SE), and attenuated internal reflection spectroscopic ellipsometry (TIRE) are promising methods in label-free biosensing applications. An ellipsometer running under surface plasmon resonance (SPR) conditions has unique advantages over other SPR-based methods in terms of sensitivity and real-time/label-free measurement capability. In this study, both SE and TIRE-based brevetoxin B (BTX) sensors were developed using two anti-BTX aptamers reported before. A new aptamer sequence was also derived from these two antiBTX aptamers using predictive modeling tools and an exclusion method. All three antiBTX aptamers' analytical performances were quite competitive in terms of both detecting range and detection limits. However, the selectivity of the previously reported aptamers against analogs of BTX was poor at low detection ranges, especially for okadaic acid. Furthermore, the selectivity of the derived aptamer was lower than its predecessors. The sensors were capable of detecting BTX in the range of 0.05 nM-1600 nM in the TIRE and 0.5 nM-2000 nM in the SE configuration. The detection limits of the sensors were 1.48 nM (1.32 ng/mL) and 0.80 nM (0.72 ng/mL) for SE and TIRE configurations, respectively. Both configurations have been used successfully to detect BTX standards spiked into real fish and shrimp samples.

A sensitive spectrophotometric ellipsometry based Aptasensor for the vascular endothelial growth factor detection.

A sensitive and selective, aptamer and spectroscopic ellipsometry based sensor is reported here for the early diagnosis of breast cancer, which is a common type of cancer following lung cancer. It was aimed to develop a single-step and label-free assay for the sensitive and selective detection of VEGF165. To this end, two different aptamers and spectroscopic ellipsometry were used. In the presented study, by determining the appropriate aptamer immobilization conditions, the spectroscopic ellipsometry technique was successfully applied for the detection of VEGF165 at the range of 1 pM-1000 pM in the buffer. Aptasensors have a detection limit of 5.81 pM and 4.29 pM, respectively.

Rheological and tribological characterization of novel modified graphene/oil-based nanofluids using force microscopy.

In this study, it is aimed to improve the lubrication and anti-wear characteristics of nanofluids produced by the distribution of silane-modified graphene nanosheets into the base oil without any surfactant or dispersant. Nanofluids are among the hottest research topics currently studied in the literature due to their interesting thermal and rheological properties. Graphene nanosheet with unique physicochemical properties is a good alternative as a nanofluid component and a lubricant. In this study, the behavior of nanofluidic films on the material was investigated by using scanning probe techniques, phase-contrast microscopy, and friction force microscopy techniques. Due to stick-slip behavior and rheological properties that are dominant in the studied ranges, problems were encountered in performing tribological analyzes with friction force microscopy. On the other hand, these results have been beneficial in determining tribological factors in nanoscale. The presented nanofluids showed non-Newtonian behavior at high concentrations and shear rates and shown an improved tribological performance up to 43% in friction coefficient, 91% in wear, and 46% in thermal conductivity compared to the base oil.

A review on nanostructure-based mercury (II) detection and monitoring focusing on aptamer and oligonucleotide biosensors.

Heavy metal ion pollution is a severe problem in environmental protection and especially in human health due to their bioaccumulation in organisms. Mercury (II) (Hg2+), even at low concentrations, can lead to DNA damage and give permanent harm to the central nervous system by easily passing through biological membranes. Therefore, sensitive detection and monitoring of Hg2+ is of particular interest with significant specificity. In this review, aptamer-based strategies in combination with nanostructures as well as several other strategies to solve addressed problems in sensor development for Hg2+ are discussed in detail. In particular, the analytical performance of different aptamer and oligonucleotide-based strategies using different signal improvement approaches based on nanoparticles were compared within each strategy and in between. Although quite a number of the suggested methodologies analyzed in this review fulfills the standard requirements, further development is still needed on real sample analysis and analytical performance parameters.

Saxitoxin aptasensor based on attenuated internal reflection ellipsometry for seafood.

In this study, we proposed label-free saxitoxin (STX) sensor using STX specific aptamer in combination with spectroscopic ellipsometry (SE) and attenuated internal reflection (AIR) spectroscopic ellipsometry method which is operated under surface plasmon resonance (SPR) conditions. Besides the other surface plasmon resonance-based applications, AIR-SE applications have unique advantages in terms of sensitivity and it was used herein for real-time detection of STX in real samples. Another method, SE, was also used and compared with AIR-SE. Analytical performances were satisfactory with low detection limits and a wide detection range. Limit of detection was 0.01 ng/mL for AIR-SE and 0.11 ng/mL for SE. Both proposed sensors were operable in 0.01 nM-1000 nM STX range. These methods were also used for the accurate, selective, and sensitive detection of STX from fish and shrimp samples.

Recent advances in aptamer-based sensors for breast cancer diagnosis: special cases for nanomaterial-based VEGF, HER2, and MUC1 aptasensors.

Cancer is one of the most common and important diseases with a high mortality rate. Breast cancer is among the three most common types of cancer in women, and the mortality rate has reached 0.024% in some countries. For early-stage preclinical diagnosis of breast cancer, sensitive and reliable tools are needed. Today, there are many types of biomarkers that have been identified for cancer diagnosis. A wide variety of detection strategies have also been developed for the detection of these biomarkers from serum or other body fluids at physiological concentrations. Aptamers are single-stranded DNA or RNA oligonucleotides and promising in the production of more sensitive and reliable biosensor platforms in combination with a wide range of nanomaterials. Conformational changes triggered by the target analyte have been successfully applied in fluorometric, colorimetric, plasmonic, and electrochemical-based detection strategies. This review article presents aptasensor approaches used in the detection of vascular endothelial growth factor (VEGF), human epidermal growth factor receptor 2 (HER2), and mucin-1 glycoprotein (MUC1) biomarkers, which are frequently studied in the diagnosis of breast cancer. The focus of this review article is on developments of the last decade for detecting these biomarkers using various sensitivity enhancement techniques and nanomaterials.

Mercuric ion detection by plasmon-enhanced spectrophotometric ellipsometer using specific oligonucleotide probes.

Pollution due to heavy metal ions, including mercury, has become a major issue because of their toxicities. It is required to monitor mercury levels in aqueous media using fast and selective methods with high accuracy. Ellipsometry is a promising technique for instance when it's combined with the plasmon resonance phenomena. We reported a biosensor system available for qualitative/quantitative determination of mercuric ions in aqueous media where both the spectrophotometric ellipsometry and oligonucleotide recognition elements were used. A single step assay using both a linear (ProbeL) and a hair-pin (ProbeH) type oligonucleotide probe as a recognition element, in addition to a sandwich-type (ProbeLS) assay were developed and compared. The detection limits were 0.23 nM, 0.03 nM and 0.15 pM for ProbeL, ProbeH and ProbeLS, respectively. The detection range was between 0.05 nM and 100 nM Hg2+ for all assays proposed herein.

Aptamer-based ellipsometric sensor for ultrasensitive determination of aminoglycoside group antibiotics from dairy products.

BACKGROUND: Residual antibiotics taken along with food consumed through the food chain are the main cause of the super-bacteria and may damage organs such as liver and kidney. Therefore, monitoring residual antibiotic levels of products in the food chain is both important and a requirement. Maximum residual limits for kanamycin and neomycin are 150 ng mL-1 and 500 ng mL-1 respectively, which are challenging for most sensor platforms. In this paper, a novel method is presented for the determination of antibiotics residues in animal-derived foods. RESULTS: Aptamer-based kanamycin and neomycin biosensors based on the spectroscopic ellipsometer and the surface plasmon resonance-enhanced total internal reflection ellipsometer methods as transducing element were developed. Detection limits of both sensor platforms were in the 0.1-1 nmol L-1 ranges, and the detection range was between the detection limit and 1000 nmol L-1 . CONCLUSION: Both ellipsometry-based aptasensors can be used as an alternative to the existing enzyme-linked immunosorbent assay-based method in terms of assay time (10 min), detection limit (0.22 ng mL-1 for neomycin and 0.048 ng mL-1 for kanamycin), and detection range. © 2020 Society of Chemical Industry.

Detection of zearalenone in an aptamer assay using attenuated internal reflection ellipsometry and it's cereal sample applications.

Mycotoxins are toxic compounds produced by the metabolism of certain fungi that threaten the food and agricultural industry. Over hundreds of mycotoxins, one of the most common toxins, zearalenone (ZEN), has toxic effects on human and animal health due to its mutagenicity, treatogenicity, carcinogenicity, nephrotoxicity, immunotoxicity, and genotoxicity. In this work, attenuated internal reflection spectroscopic ellipsometry (AIR-SE) combined with the signal amplification via surface plasmon resonance conditions that were proved to be a highly sensitive analytical tool in bio-sensing was developed for the sensitive and selective ZEN detection in cereal products such as corn, wheat, rice, and oat. Combined with the oligonucleotide aptamer for ZEN recognition, our proposed method showed good performance with yielding 0.08 ng/mL LOD and 0.01-1000 ng/mL detection range. A mini-review was also introduced in, to compare various methods for ZEN detection.

Spectrophotometric ellipsometry based Tat-protein RNA-aptasensor for HIV-1 diagnosis.

Rapid and reliable diagnosis of Human Immunodeficiency Virus (HIV) Type I that causes autoimmune deficiency syndrome (AIDS) is still important today. In this study, the HIV-I Tat (trans-activator of transcription) protein-specific RNA-aptamer (antiTat) and spectroscopic ellipsometer were preferred to increase specificity and sensitivity in the diagnosis. The ellipsometry is a well-known characterization tool for the ultra-thin films, where polarization state changes show surface deposition in terms of the ellipsometric angles, psi (Ψ) and delta (Δ). Here, we reported the HIV-Tat protein detection performance of antiTat aptamers both for the spectroscopic ellipsometry (SE) and for the surface plasmon resonance enhanced total internal reflection ellipsometry (SPReTIRE), first time. Detection limits for antiTat aptamers with various configurations were in the range of nM-pM protein in the buffer solution. For instance, SPRe-TIRE configuration revealed a detection limit of 1 pM (or about 1.5 pg/mL) for HIV-Tat protein in the range of 1.0-500 nM.

Topographic characterization of unworn contact lenses assessed by atomic force microscopy and wavelet transform.

This paper analyses the three-dimensional (3-D) surface morphology of optic surface of unworn contact lenses (CLs) using atomic force microscopy (AFM) and wavelet transform. Refractive powers of all lens samples were 2.50 diopters. Topographic images were acquired in contact mode in air-conditioned medium (35% RH, 23°C). Topographic measurements were taken over a 5 µm × 5 µm area with 512 pixel resolution. Resonance frequency of the tip was 65 kHz. The 3-D surface morphology of CL unworn samples revealed (3-D) micro-textured surfaces that can be analyzed using (AFM) and wavelet transform. AFM and wavelet transform are accurate and sensitive tools that may assist CL manufacturers in developing CLs with optimal surface characteristics.

A novel Surface Plasmon Resonance enhanced Total Internal Reflection Ellipsometric application: electrochemically grafted isophthalic acid nanofilm on gold surface.

The scope of this study is to modify a Surface Plasmon Resonance (SPR) sensor slide with isophthalic acid to evaluate the possible application on the detection of copper(II) ions in aqueous media by total internal reflection ellipsometry. A gold sensor surface was modified by an electrochemical diazonium reduction modification method. The modified surfaces are characterized with cyclic voltammetry (CV) and ellipsometry. Isophthalic acid monolayer modified gold slides were used for in situ detection of aqueous Cu(2+) solution with the SPR enhanced total internal reflection ellipsometry (SPRe-TIRE) technique. Layer formation, pH dependency of adsorption, sensor response of the SPRe-TIRE and isothermal kinetic parameters were examined. A high dependency on the number of CV cycles in the monolayer-multiple layer transition was observed. The suggested sensor gave a linear response over a wide range of Cu(2+) concentrations. It was also reported that adsorption on the SPRe-TIRE sensor gave Langmuir adsorption model behavior.