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Targeted radiopharmaceuticals offer the possibility of improved imaging with reduced side effects. Up to now, a variety of biological receptors such as aptamers have been successfully radiolabeled and applied to diagnostic imaging of cancers. The concept of using radio-labeled aptamers for binding to their targets has stimulated an immense body of research in diagnostic nuclear medicine. These biological recognition elements are single-stranded oligonucleotides that interact with their target molecules with high affinity and specificity in unique three-dimensional structures. Because of their high affinity and specificity, the receptor-binding aptamers labeled with gamma emitters such as 99mTc, 64Cu, 111In, 18F and 67Ga can facilitate the visualization of receptor-expressing tissues noninvasively. Compared to the antibody-based radiopharmaceuticals, the radiolabeled aptamers provide a number of advantages for clinical diagnostics including high stability, low cost, and ease of production and modification, low immunogenicity and, especially, superior tissue penetration because of their smaller size. In this review, we present recent progresses and challenges in aptamer-based diagnostic radiopharmaceuticals and highlight some representative applications of aptamers in nuclear medicine. [ABSTRACT FROM AUTHOR]

Abstract In this study, a high-performance biosensing nanoplatform based on amidoxime-modified polyacrylonitrile nanofibers decorated with Ag nanoparticles (AgNPs-PAN-oxime NFs) is described. The AgNPs-PAN-oxime NFs were prepared by the combination of electrospinning technique and chemical modification of nitrile group in the PAN. The proposed signal amplifiying nanoplatform was applied in the fabrication of an electrochemical aptasensor for the sensitive detection of CA 125 based on aptamer-cDNA duplex and target induced strand displacement recognition mechanism. The aptasensing interface offers high sensitivity and selectivity for detection of tumor marker due to inherent advantages such as high specific surface area of NFs, good conductivity by doping AgNPs into the polymer NFs and especially the ideal selectivity of anti CA 125 aptamer to its target. The electrochemical aptasensor revealed a wide dynamic linear range (DLR) from 0.01 to 350 U mL−1 with a correlation coefficient of 0.991 and limit of detection (LOD) of 0.0042 U mL−1. Additionally, the designed aptasensor showed acceptable selectivity, reproducibility, repeatability and stability. The satisfactory results for determination of CA 125 in serum samples compared to ELISA method (p -value > 0.05) indicated the potential application of aptasensor in clinical monitoring of tumor biomarker for early diagnosis and management of ovarian cancer. Graphical abstract Unlabelled Image Highlights • In this study, a high-performance biosensing nanoplatform based on amidoxime-modified polyacrylonitrile nanofibers decorated with Ag nanoparticles (AgNPs-PAN-oxime NFs) was introduced. • The described nanoplatform was utilized in a displacement electrochemical aptasensor for detection of CA 125 in ovarian cancer patients. • The electrochemical aptasensor revealed a wide dynamic linear range from 0.01 to 350 U mL-1 and a limit of detection of 0.0042 U mL-1. [ABSTRACT FROM AUTHOR]

Recent developments in biotechnology offer the new methods for the sensitive detection of heavy metals based on the affinity and specificity of aptamers, as nucleic acid ligands selected from random sequence pools in vitro. Heavy metals have received considerable importance as the most toxic metallic pollutants which may cause serious environmental damages. They are classified as trace elements because of their presence in trace concentrations in various environmental matrices. Thus, the precise and sensitive methods to detect heavy metals are important to ensure human and environment safety. Aptamers as the biological probes, show high binding affinity which can often be directly translated into high detection sensitivity. On the other hand, high selectivity and stability make them possible to detect a wide range of targets, especially metallic ions. This review provides current progress of aptamers for environmental and biological monitoring of heavy metals using the nanomaterials mainly in two groups: (i) aptamer based biosensors (aptasensors) and (ii) aptamer based biosorbents (aptasorbents). The introduction of nanomaterials can efficiently increase the immobilization quantity of aptamers. Furthermore, they play an important role in the orientation and assembly density controlling of aptamers for the optimized recognition ability. [ABSTRACT FROM AUTHOR]

Lead (Pb) as a topically poisonous metal represents a serious threat to the ecological environment and especially to human beings. Therefore, it is urgent to develop a rapid and reliable monitoring technique for this heavy metal in the environmental samples. In the present study, we have designed a selective and sensitive method for the determination of ultratrace contents of Pb 2 + in biological samples, based on the guanine (G)-quadruplex formed by the aptamer with hairpin structure and Pb 2 + . For this purpose, Pb 2 + specific aptamer serving as affinity probe to capture and separate trace amounts of the analyte, was covalently linked to Fe 3 O 4 /graphene oxide (GO) surface by using a suitable cross-linking agent. Then, the G-quadruplex complex was formed by the opening of the “neck- ring” of the hairpin structure of aptamer in the presence of Pb 2 + . Inductively coupled plasma mass spectrometry (ICP-MS) was used for determination of Pb 2 + in biological matrices. The analysis conditions were optimized and the performance of the proposed method was investigated. Under optimum conditions, the calibration curve was linear over the range of 0.3–867.5 μg L − 1 and an enrichment factor (EF) of 50 was obtained. The limit of detection (LOD) was 0.05 μg L − 1 and the relative standard deviation (RSD) for single-sorbent repeatability and sorbent-to-sorbent reproducibility were < 4.7% and 8.8% (n = 5), respectively. The accuracy of aptamer-based affinity purification method was confirmed by the analysis of quality control materials (QCMs, Seronorm™ Blood REF NO 201505 and Urine REF NO 2525). [ABSTRACT FROM AUTHOR]

[Display omitted] • An electrochemical genosensor based on the format of aptamer/melphalan/FC-COOH/GNC-TAC/paper electrode for the Pb ions detection. • Remarkable advantages including high selectivity and wide detectable range. • The good consistency of the results obtained with the aptasensor and those by the QCM analysis and GF-AAS technique. We report a voltammetric aptasensor based on the graphite nanocrystals in a bed of tetrahedral amorphous carbon (GNC-TAC) and guanine (G)-rich aptamers alkylated with melphalan anticancer for determination of ultratrace Pb2+ in the clinical samples. In this work, an adhesive and stable layer of GNC-TAC was formed on the cellulose paper by the ion beam sputtering deposition (IBSD) method. This porous conductive nanographite film plays a key role in providing a large area for adsorption of ferrocene carboxylic acid (FC-COOH) anticancer as a redox indicator. Then, melphalan that attaches the alkyl groups to the guanine bases of DNA aptamer was bonded covalently to the carboxylic groups of FC-COOH via the aid of EDC/NHS. The introduction of Pb2+ ions to the aptamer/melphalan/FC-COOH/GNC-TAC/paper electrode leads to the formation of a G-quadruplex (G4)/Pb2+ complex and dissociation of this complex from the modified electrode surface. The target-induced aptamer release from melphalan/FC-COOH/GNC-TAC/paper electrode makes the sensing interface smaller which results in an increase in the current signal. Based on this signal-on mechanism, the sensitive detection of Pb2+ ions in the dynamic linear range (DLR) of 0.5–700.0 μg L−1 is realized (limit of detection (LOD): 0.15 μg L−1). The present strategy shows remarkable advantages including high selectivity and wide detectable range. More importantly, the good consistency of the results obtained with the aptasensor and those by the quality control material (QCM) analysis and atomic absorption spectroscopy equipped with graphite furnace (GF-AAS) technique showed that the proposed strategy has a high potential for Pb2+ detection in the clinical samples. [ABSTRACT FROM AUTHOR]

The authors describe an electrochemical aptamer based assay for the determination of the serine protease lysozyme in very low (pM) concentrations. The method is based on the formation of a complex between anti-lysozyme aptamer fragments and lysozyme, and on electrochemical detection by differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The surface of a glassy carbon electrode was modified with a nanocomposite consisting of gold nanoparticles and electrochemically reduced graphene oxide nanosheets (AuNPs/erGO), and the thiolated aptamer was then linked to the AuNPs by self-assembly through Au-S bonds. The interaction of immobilized aptamers with lysozyme leads to the decreased peak current in DPV and increased charge transfer resistance (R) in EIS when using hexacyanoferrate or Methylene Blue as a redox probe. The calibration plot, when applying EIS and working at a typical voltage of −0.22 V (vs. SCE), is linear over 1.0 to 104.3 pM concentration range, with a detection limit of 0.06 pM (at a signal-to-noise ratio of 3). The respective data for DPV are a 9.6-205.5 pM linear range with a detection limit of 0.24 pM. Depending on the redox marker applied, the method works in the 'signal-off' or 'signal-on' mode in DPV and EIS protocols, respectively. The sensing interface is high specific for lysozyme and not affected by other proteins. The method was applied to the determination of lysozyme in spiked diluted human serum, and the results agreed well with data obtained with a standard ELISA. [ABSTRACT FROM AUTHOR]

In this work, a label free electrochemical aptasensor for the detection of ultra-traces of vascular endothelial growth factor (VEGF 165 ) based on “signal off” and “signal on” mechanisms of response was developed. The BSA-gold nanoclusters/ionic liquid (BSA-AuNCs/IL) was used as a suitable nanocomposite platform for immobilization of the aptamer on a glassy carbon electrode. In “signal off” mechanism, the interaction of VEGF 165 with its anti-VEGF 165 aptamers, resulted in desorption of methylene blue (MB) probe from aptamer and its release into solution. Consequently, the decrease in current intensity of the differential pulse voltammogram of adsorbed MB was monitored and found to be linearly proportional with increasing concentration of VEGF 165 in sample solution in the range of 1–120 pM with a limit of detection of 0.32 pM. While, in “signal on” mechanism, the interaction of immobilized anti-VEGF 165 aptamers on the electrode surface with VEGF 165 , led to more mass-transfer limiting of the [Fe(CN) 6 ] 3−/4− probe to the electrode surface. Therefore, the charge transfer resistance ( R ct ) of the probe was increased linearly with increasing concentration of VEGF 165 in the range of 2.5–250 pM with a limit of detection of 0.48 pM. The experimental results demonstrated that both of these mechanisms are suitable for determination of low levels of the VEGF 165 tumor marker in serum samples. [ABSTRACT FROM AUTHOR]