Aptasensor for lead(II) based on the use of a quartz crystal microbalance modified with gold nanoparticles

Studies on the Aptasensor Miniaturization for Electrochemical Detection of Lead Ions

Lead poses severe effects on living organisms, and since Pb2+ ions tend to accumulate in different organs, it is crucial to monitor Pb2+ concentration in samples such as water and soil. One of the approaches is the utilization of biosensors combined with aptamer-based layers for the electrochemical detection of lead ions. Herein, we present the studies of applying miniaturized screen-printed transducers as solid surfaces to fabricate aptamer layers. As the research is the direct continuation of our previous studies regarding the use of gold disk electrodes, the working parameters of elaborated aptasensors were defined, including the range of linear response (10-100 nM), selectivity as well as stability, regeneration, and feasibility of application for the analysis of real samples. This was achieved using voltammetric techniques including cyclic and square-wave voltammetry in the presence of methylene blue redox indicator.

A Novel Fluorescent Aptasensor for Arsenic(III) Detection Based on a Triple-Helix Molecular Switch

A novel aptamer-based fluorescent-sensing platform with a triple-helix molecular switch (THMS) was proposed as a switch for detecting the arsenic(III) ion. The triple helix structure was prepared by binding a signal transduction probe and arsenic aptamer. Additionally, the signal transduction probe labeled with fluorophore (FAM) and quencher (BHQ1) was employed as a signal indicator. The proposed aptasensor is rapid, simple and sensitive, with a limit of detection of 69.95 nM. The decrease in peak fluorescence intensity shows a linear dependence, with the concentration of As(III) in the range of 0.1 µM to 2.5 µM. The whole detection process takes 30 min. Moreover, the THMS-based aptasensor was also successfully used to detect As(III) in a real sample of Huangpu River water with good recoveries. The aptamer-based THMS also presents distinct advantages in stability and selectivity. The proposed strategy developed herein can be extensively applied in the field of food inspection.

A novel metal-organic frameworks composite-based label-free point-of-care quartz crystal microbalance aptasensing platform for tetracycline detection

A novel label-free point-of-care quartz crystal microbalance (QCM) aptasensing platform based on metal-organic frameworks (MOFs) and gold nanoparticles (AuNPs) was fabricated for tetracycline (TC) detection. MOFs (HKUST-1) and AuNPs were modified onto the sensing interface of QCM sensor to enhance the sensing performance of the QCM aptasensor. TC aptamer with sulfhydryl group was fixed through Au-S bond. The recognition performance of the aptasensor was predicted and verified by the computer simulation. At the optimal conditions, the frequency change of the sensor was adopted for quantitative detection of TC. The prepared QCM aptasensor exhibited a wide linear range from 1 × 10^-10 g mL^-1 to 1 × 10^-5 g mL^-1 with low limit of detection (0.8 × 10^-11 g mL^-1). High sensitivity, good selectivity, acceptable recoveries (87.6-91.4%) in real samples were obtained. For the first time, MOFs were utilized in the construction of QCM aptasensing platform, providing a promising application way of MOFs in the QCM sensing.

Gold Nanoparticles as Antimicrobial Agents: A Mini-Review

Metal nanoparticles, such as gold nanoparticles, have abundant unusual chemical and physical properties owing to the effects of their quantum size and their large surface area, in comparison with other metal atoms. Gold nanoparticles (AuNPs), in particular, are becoming increasingly popular due to their biocompatibility, multifunctional and aqueous solubility. Many scientific reports described the important antimicrobial properties possessed by the gold nanoparticles. Therefore, the present mini-review summarizes an overview of gold nanoparticles as broad spectrum antimicrobial agents for biomedical applications.

An overview of Structured Biosensors for Metal Ions Determination

The determination of metal ions is important for nutritional and toxicological assessment. Atomic spectrometric techniques are highly efficient for the determination of these species, but the high costs of acquisition and maintenance hinder the application of these techniques. Inexpensive alternatives for metallic element determination are based on dedicated biosensors. These devices mimic biological systems and convert biochemical processes into physical outputs and can be used for the sensitive and selective determination of chemical species such as cations. In this work, an overview of the proposed biosensors for metal ions determination was carried out considering the last 15 years of publications. Statistical data on the applications, response mechanisms, instrumentation designs, applications of nanomaterials, and multielement analysis are herein discussed.

Advances in aptamer screening and aptasensors' detection of heavy metal ions

Heavy metal pollution has become more and more serious with industrial development and resource exploitation. Because heavy metal ions are difficult to be biodegraded, they accumulate in the human body and cause serious threat to human health. However, the conventional methods to detect heavy metal ions are more strictly to the requirements by detection equipment, sample pretreatment, experimental environment, etc. Aptasensor has the advantages of strong specificity, high sensitivity and simple preparation to detect small molecules, which provides a new direction platform in the detection of heavy metal ions. This paper reviews the selection of aptamers as target for heavy metal ions since the 21th century and aptasensors application for detection of heavy metal ions that were reported in the past five years. Firstly, the selection methods for aptamers with high specificity and high affinity are introduced. Construction methods and research progress on sensor based aptamers as recognition element are also introduced systematically. Finally, the challenges and future opportunities of aptasensors in detecting heavy metal ions are discussed.

A Facile Aptasensor for Instantaneous Determination of Cadmium Ions Based on Fluorescence Amplification Effect of MOPS on FAM-Labeled Aptamer

Analytical performance and efficiency are two pivotal issues for developing an on-site and real-time aptasensor for cadmium (Cd²⁺) determination. However, suffering from redundant preparations, fabrications, and incubation, most of them fail to well satisfy the requirements. In this work, we found that fluorescence intensity of 6-carboxyfluorescein(FAM)-labeled aptamer (FAM-aptamer) could be remarkably amplified by 3-(N-morpholino)propane sulfonic acid (MOPS), then fell proportionally as Cd²⁺ concentration introduced. Importantly, the fluorescence variation occurred immediately after addition of Cd²⁺, and would keep stable for at least 60 min. Based on the discovery, a facile and ultra-efficient aptasensor for Cd²⁺ determination was successfully developed. The sensing mechanism was confirmed by fluorescence pattern, circular dichroism (CD) and intermolecular interaction related to pK_a. Under the optimal conditions, Cd²⁺ could be determined rapidly from 5 to 4000 ng mL^-1. The detection limit (1.92 ng mL^-1) was also lower than the concentration limit for drinking water set by WHO and EPA (3 and 5 ng mL^-1, respectively). More than a widely used buffer, MOPS was firstly revealed to have fluorescence amplification effect on FAM-aptamer upon a given context. Despite being sensitive to pH, this simple, high-performance and ultra-efficient aptasensor would be practical for on-site and real-time monitoring of Cd²⁺.

An Electrochemical Aptasensor for Pb2+ Detection Based on Metal-Organic-Framework-Derived Hybrid Carbon

A new double-shelled carbon nanocages material was synthesized and developed an aptasensor for determining Pb²⁺ in aqueous solution. Herein, nanoporous carbon materials derived from core–shell zeolitic imidazolate frameworks (ZIFs) demonstrated excellent electrochemical activity, stability, and high specificity surface area, consequently resulting in the strong binding with aptamers. The aptamer strands would be induced to form G-quadruplex structure when Pb²⁺ was introduced. Under optimal conditions, the aptasensor exhibited a good linear relationship of Pb²⁺ concentration ranging from 0.1 to 10 μg L⁻¹ with the detection limits of 0.096 μg L⁻¹. The feasibility was proved by detecting Pb²⁺ in spiked water samples and polluted soil digestion solution. The proposed aptasensor showed excellent selectivity and reproducibility, indicating promising applications in environmental monitoring.

Volatile organic compounds gas sensor based on quartz crystal microbalance for fruit freshness detection: A review

In this review article, the state of the art of gas sensors based on quartz crystal microbalance (QCM) for fruit freshness detection is overviewed from the aspects of development history, working principle, selection and modification of sensitive materials, and volatile organic compounds detection of fruits. According to the characteristics of respiratory intensity at the stage of fruit ripening, fruits can be divided into respiration climacteric fruits and non-climacteric fruits. In recent years, research has mainly focused on respiration climacteric fruits, such as bananas and mangoes, etc., while related studies on non-climacteric fruits have been rarely reported, except for citrus fruits. The preparation methods and structure design of sensitive materials based on physical/chemical adsorption mechanisms are further discussed according to the odor components that affect the freshness of fruits, namely alkenes, esters, aldehydes and alcohols.

Nanomaterial based aptasensors for clinical and environmental diagnostic applications

Nanomaterials have been exploited extensively to fabricate various biosensors for clinical diagnostics and food & environmental monitoring. These materials in conjugation with highly specific aptamers (next-gen antibody mimics) have enhanced the selectivity, sensitivity and rapidness of the developed aptasensors for numerous targets ranging from small molecules such as heavy metal ions to complex matrices containing large entities like cells. In this review, we highlight the recent advancements in nanomaterial based aptasensors from the past five years also including the basics of conventionally used detection methodologies that paved the way for futuristic sensing techniques. The aptasensors have been categorised based upon these detection techniques and their modifications viz., colorimetric, fluorometric, Raman spectroscopy, electro-chemiluminescence, voltammetric, impedimetric and mechanical force-based sensing of a multitude of targets are discussed in detail. The bio-interaction of these numerous nanomaterials with the aptameric component and that of the complete aptasensor with the target have been studied in great depth. This review thus acts as a compendium for nanomaterial based aptasensors and their applications in the field of clinical and environmental diagnosis.

Piezoelectric arsenite aptasensor based on the use of a self-assembled mercaptoethylamine monolayer and gold nanoparticles

The authors describe a piezoelectric aptasensor for arsenite. A self assembeled monolayer (SAM) of mercaptoethylamine was prepared to immobilize arsenite on the surface of a quartz crystal microbalance. Gold nanoparticles were modified with arsenite aptamer to amplify the response frequency of the biosensor. Arsenite first binds to the SAM on the gold surface of the QCM. On addition of gold nanoparticles with aptamer (DNA-AuNp), the SAM-As(III)-aptamer sandwich is formed. This increases the resonance frequency of the sensor and allows trace concentration of arsenite to be determined. The aptasensor can detect arsenite in the 8 to 1000 nmol·L^-1 concentration range with a 4.4 nmol·L^-1 lower detection limit (at S/N = 3). The sandwich structure improves the specificity of the aptasensor without considering the conformational transition of the aptamer. The strategy described here conceivably has a large potential as it shows that small molecules can be sensed by using aptamers with unknown working mechanism. Graphical abstract Schematic presentation of a piezoelectric biosensor for arsenite detection by using a mercaptoethylamine monolayer and gold nanoparticles with respect to Arsenite first binds to the SAM on the gold surface of the QCM. Next, gold nanoparticles with aptamer (DNA-AuNp) are added to form a SAM-As(III)-aptamer sandwich which affects the resonance frequency.

Applications of Gold Nanoparticles in Non-Optical Biosensors

Due to their unique properties, such as good biocompatibility, excellent conductivity, effective catalysis, high density, and high surface-to-volume ratio, gold nanoparticles (AuNPs) are widely used in the field of bioassay. Mainly, AuNPs used in optical biosensors have been described in some reviews. In this review, we highlight recent advances in AuNP-based non-optical bioassays, including piezoelectric biosensor, electrochemical biosensor, and inductively coupled plasma mass spectrometry (ICP-MS) bio-detection. Some representative examples are presented to illustrate the effect of AuNPs in non-optical bioassay and the mechanisms of AuNPs in improving detection performances are described. Finally, the review summarizes the future prospects of AuNPs in non-optical biosensors.

An aptamer-based colorimetric lead(II) assay based on the use of gold nanoparticles modified with dsDNA and exonuclease I

The authors describe a colorimetric method for the sensitive and selective detection of Pb(II). It is based on the use exonuclease I (Exo I), a Pb(II)-binding aptamer bound to gold nanoparticles (AuNPs), and a DNA strand that complementary to the aptamer. In the absence of Pb(II), the dsDNA on the AuNPs prevents aggregation of the AuNPs in the presence of NaCl. In the presence of Pb(II), however, the aptamer binds Pb(II) and complementary strand is released and digested by Exo I. As a result, the solution of AuNPs undergoes a color change from red to purple if salt is added to the sample. The assay is selective for Pb(II) and has a limit of detection as low as 2.4 nM. It was successfully applied to the determination of Pb(II) in spiked tap water. Graphical abstract Schematic presentation of the aptamer based method for Pb²⁺ detection via salt-induced aggregation of gold nanoparticles and colorimetric quantitation.