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Herein, a novel colorimetric aptasensor was introduced for detection of cocaine based on the formation of three-way junction pockets on the surfaces of gold nanoparticles (AuNPs) and the catalytic activity of the surfaces of AuNPs. Simplicity and detection of cocaine in a short time (only 35 min) are some of the unique features of the proposed sensing strategy. In the presence of cocaine, triple-fragment aptamer (TFA) forms on the surfaces of AuNPs, leading to a significant decrease of the catalytic activity of AuNPs and the color of samples remains yellow. In the absence of target, TFA does not form on the surfaces of AuNPs and 4-Nitrophenol, as a colorimetric agent, has more access to the surfaces of AuNPs, resulting in the reduction of 4-Nitrophenol and the color of sample changes from yellow to colorless. The sensing strategy showed good specificity, a limit of detection (LOD) of 440 pM and a dynamic range over 2–100 nM. The sensing method was also successfully applied to detect cocaine in spiked human serum samples with recovery of 94.71–98.63%.

Simple and reliable sensors for detection of arsenic (As), a toxic heavy metal, in drinking water and blood serum are highly desirable. Herein, we reported the fabrication and characterization of a fluorescent aptasensor for the detection of As (III) using target-induced conformational change of the Biotin and FAM-labeled complementary strand of aptamer (CS1), silica nanoparticles coated with streptavidin (SNPs-Streptavidin) and a label-free aptamer (Apt). The sensor described here had several attractive features, such as simplicity, rapid response and use of label-free Apt. Upon addition of As (III), Apt released its CSs and CS1 formed a hairpin structure on the surface of SNPs-Streptavidin, leading to a strong fluorescence signal. Without introduction of As (III), Apt was hybridized with its CSs and a weak fluorescence signal was obtained. The sensor exhibited a wide linear range between 2 and 500 nM and a very low detection limit of 0.45 nM. In addition, the applicability of the developed method was tested using spiked tap water and serum samples with satisfactory results.

Herein, a sensitive and rapid fluorescent aptasensor was developed for the detection of cocaine as an illicit drug, based on an amplification strategy involving the use of silica nanoparticles coated with streptavidin (SNPs), double quenching of FAM fluorophore and cocaine split aptamer. Presence of cocaine could trigger the formation of the double-fragment cocaine aptamer and bring TAMRA fluorophore near the SNP surface and FAM close to BHQ-1 and TAMRA, resulting in the enhancement of relative fluorescence signal (fluorescence intensity of TAMRA/fluorescence intensity of FAM). Under optimal conditions, the proposed aptasensor achieved a limit of detection (LOD) of 84 pM and a linear range of 500 pM to 80 nM for cocaine. The practical potential of the developed sensing platform was proved by the detection of cocaine in spiked human serum samples with satisfactory recoveries.

Detection and quantitation of interferon-gamma (IFN-γ) in blood is of vital importance for diagnosis of latent tuberculosis. The authors describe an electrochemical aptasensor for IFN-γ that is based on a triple-helix molecular switch (THMS). The combination of a THMS with amperometry makes the sensor selective, sensitive and fast (50 min). In the presence of IFN-γ, the structure of the THMS is disassembled and the electrochemical probes, Methylene Blue (MB), can only bind to the signal transduction probe (STP) on the surface of the gold electrode, this leading to a weak peak current. However, in the absence of IFN-γ, the structure of THMS is preserved and MB can interact with the THMS to result in strong current (typically measured at −0.24 V vs. silver reference electrode). Under optimized conditions, the assay has a 3 pg·mL−1 detection limit and a linear range that extends from 10 to 1500 pg·mL−1. Employed to the determination of IFN-γ in spiked serum samples, it gave recoveries that ranged from 91.3% to 102.8%.

There is a prompt need for determination of aflatoxin B1 (AFB1) in food products to avoid distribution and consumption of contaminated food products. In this study, an accurate electrochemical sensing strategy was presented for detection of AFB1 based on aptamer (Apt)-complementary strands of aptamer (CSs) complex which forms a π-shape structure on the surface of electrode and exonuclease I (Exo I). The presence of π-shape structure as a double-layer physical barrier allowed detection of AFB1 with high sensitivity. In the absence of AFB1, the π-shape structure remained intact, so only a weak peak current was recorded. Upon the addition of AFB1, the π-shape structure was disassembled and a strong current was recorded following the addition of Exo I. Under optimal conditions, the electrochemical signals enhanced as AFB1 concentrations increased with a dynamic range of 7-500pg/mL and a limit of detection (LOD) of 2pg/mL. The developed aptasensor was also used to analyze AFB1 spiked human serum and grape juice samples and the recoveries were 95.4-108.1%.

Determination of fluoroquinolones (FQs) in foodstuffs and environment is of great importance. In this study, a novel electrochemical sensing method was developed for rapid, highly sensitive and specific detection of FQs, based on aptamer (Apt) as molecular recognition probe, single-stranded DNA-binding protein (SSB) as a physical and negatively charged barrier for the access of redox probe ([Fe(CN)6]3−/4−) to the surface of gold electrode. The designed electrochemical aptasensor needs less than 1 h for detection of ciprofloxacin. In the absence of ciprofloxacin, SSB interacts with Apt and restricts the access of redox probe to the surface of electrode, leading to a weak current signal. In the presence of target, SSB could not bind to the Apt, resulting in more access of redox probe to the surface of electrode and a strong current signal. The designed electrochemical sensor exhibited high specificity toward FQs with a limit of detection (LOD) as low as 263 pM for ciprofloxacin. Moreover, the developed sensing method was successfully applied for determination of ciprofloxacin in serum, milk and water samples with LODs of 336, 351 and 261 pM, respectively.

The clinical administration of epirubicin (Epi) in the treatment of cancer has been restricted, owing to its cardiotoxicity. Targeted delivery of anticancer agents could increase their therapeutic efficacy and decrease their off-target effects. In this study, a novel Epi-DNA diamond nanostructure (DDN) conjugate containing two kinds of aptamers (MUC1 and ATP aptamers) was designed and evaluated in the treatment of target cells, including C26 cells (murine colon carcinoma cell) and MCF-7 cells (breast cancer cell). DDN and Epi-DDN conjugate formations were analyzed by gel retardation assay and fluorometric analysis, respectively. Release profiles of Epi from the developed Epi-DDN conjugate were evaluated at pHs 5.4 and 7.4. For the MTT assay (cell viability study), CHO cells (Chinese hamster ovary cell, nontarget), C26 and MCF-7 cells (target) were treated with the Epi-DDN conjugate, DDN, Epi, Epi-DDN conjugate without ATP aptamer and Epi-DDN conjugate without MUC1 aptamer. Internalization of the Epi-DDN conjugate was assessed by flow cytometry analysis and fluorescence imaging. Finally, the designed Epi-DDN conjugate was utilized for inhibition of tumor growth in vivo. 10 μM Epi was efficiently loaded in 1 μM DDN. The drug was released from the Epi-DDN conjugate in a pH-sensitive manner (higher release in acidic conditions). The results of flow cytometry analysis and fluorescence imaging confirmed that the developed Epi-DDN conjugate was effectively internalized into target cells, but not into nontarget cells. The results of the MTT assay were consistent with the internalization data. The Epi-DDN conjugate had more cytotoxicity in MCF-7 and C26 cells and less cytotoxicity in CHO cells in comparison with Epi alone. Moreover, the Epi-DDN conjugate could effectively prohibit tumor growth in vivo.

In this study, a sensor is described for determination of patulin by using ratiometric fluorescence measurement and strand displacement strategy. In the presence of patulin, the ratiometric fluorescence response decreases, owing to disassembly of DNA duplex structure and target-mediated release of TAMRA-labeled complementary DNA sequence2 (cDNA2). While, in the absence of target, the fluorescence resonance energy transfer (FRET) phenomenon happens between FAM and TAMRA under excitation at 490 nm, resulting in the enhancement of ratiometric signal. The use of ratiometric fluorescence signal with different signal indicators avoids the problem of environmental interference and improves the sensitivity of the aptasensor. Also, the DNA duplex structure contains minimum aptamer-involved base pair sequence, resulting in further improvement of the aptasensor sensitivity. This sensing platform provided a wide linear range from 15 ng/L to 35 μg/L and a detection limit of 6 ng/L for patulin. The aptasensor was used to determine patulin in spiked apple juice samples and showed satisfactory results.

Analytical methods for detection and quantitation of chloramphenicol in blood serum and foodstuffs arse highly in demand. In this study, a colorimetric sandwich aptamer-based sensor (aptasensor) was fabricated for sensitive and selective detection of chloramphenicol, based on an indirect competitive enzyme-free assay using gold nanoparticles (AuNPs), biotin and streptavidin. The designed aptasensor acquires characteristics of AuNPs, including large surface area and unique optical properties, and strong interaction of biotin with streptavidin. In the absence of chloramphenicol, the sandwich structure of aptasensor forms, leading to the observation of sharp red color. In the presence of target, functionalized AuNPs could not bind to 96-well plates, resulting in a faint red color. The fabricated colorimetric aptasensor exhibited high selectivity toward chloramphenicol with a limit of detection as low as 451 pM. Moreover, the developed colorimetric aptasensor was successfully used to detect chloramphenicol in milk and serum with LODs of 697 and 601 pM, respectively.

Measurement of myoglobin (Mb) in human blood serum is of great interest for quick diagnosis of acute myocardial infarction (AMI). In this study, a novel fluorescent aptasensor was designed for ultrasensitive and selective detection of Mb, based on target-induced high fluorescence intensity, complementary strand of aptamer (CS), PicoGreen (PG) dye, exonuclease III (Exo III) and silica nanoparticles coated with streptavidin (SNPs-Streptavidin). The developed aptasensor obtains characteristics of SNPs as enhancers of fluorescence intensity, Exo III as an enzyme which selectively digests the 3'-end of double-stranded DNA (dsDNA), PG as a fluorescent dye which could selectively bind to dsDNA and high selectivity and sensitivity of aptamer (Apt) toward its target. In the absence of Mb, no free CS remains in the environment of SNPs-Streptavidin, resulting in a weak fluorescence emission. In the present of Mb, dsDNA-modified SNPs-Streptavidin complex forms, leading to a very strong fluorescence emission. The developed fluorescent aptasensor exhibited high specificity toward Mb with a limit of detection (LOD) as low as 52 pM. In addition, the designed fluorescent aptasensor was efficiently used to detect Mb in human serum.

Clinical use of daunorubicin (Dau) in treatment of leukemia has been restricted because of its cardiotoxicity. Targeted delivery of anticancer drugs could decrease their off-target effects and enhance their efficacy. In this study a modified polyvalent aptamers (PA)-Daunorubicin (Dau)-Gold nanoparticles (AuNPs) complex was designed and its efficacy was assessed in Molt-4 cells (human acute lymphoblastic leukemia T-cell, target). Dau was efficiently loaded (10.5 μM) onto 1mL of PA-modified AuNPs. Dau was released from the PA-Dau-AuNPs complex in a pH-sensitive manner (faster release at pH5.5). The results of flow cytometry analysis indicated that the PA-Dau-AuNPs complex was efficiently internalized into target cells, but not into nontarget cells. The results of MTT assay were consistent with the internalization data. PA-Dau-AuNPs complex had less cytotoxicity in U266 cells compared to Dau alone and even Apt-Dau-AuNPs complex. The PA-Dau-AuNPs complex had more cytotoxicity in Molt-4 cells compared to Dau alone and even Apt-Dau-AuNPs complex. Cytotoxicity of PA-Dau-AuNPs complex was effectively antagonized using antisense of polyvalent aptamers. In conclusion, the designed drug delivery system inherited the properties of efficient drug loading, tumor targeting, pH-dependent drug release and controllable delivery of Dau to tumor cells.

Cocaine is one of the most commonly abused stimulant which could affect the central nervous system. In this work, an electrochemical aptasensor was designed for sensitive and selective detection of cocaine, based on complimentary strands of aptamer (CSs), H-shape structure of Aptamer (Apt)-CSs conjugate and gold electrode. This aptasensor inherits properties of gold such as high electrochemical conductivity and large surface area, as well as high selectivity and sensitivity of aptamer toward its target and property of H-shape structure of Apt-CSs conjugate to act as a gate for the access of redox probe to the surface of electrode. In the absence of cocaine, the gate is closed, so that the electrochemical signal is weak. In the presence of cocaine, aptamer binds to target, leaves the surface of electrode and the gate is opened, leading to a strong electrochemical signal. The fabricated electrochemical aptasensor exhibited good selectivity toward cocaine with a limit of detection (LOD) as low as 0.228 nM. Furthermore, the designed aptasensor was successfully used to detect cocaine in serum with a LOD as low as 0.273 nM.

Detection and quantitation of antibiotic residues in blood serum and animal foodstuffs are of great significance. In this study, an electrochemical aptasensor was developed for sensitive and selective detection of streptomycin, based on exonuclease I (Exo I), complimentary strand of aptamer (CS), Arch-shape structure of aptamer (Apt)-CS conjugate and gold electrode. The designed aptasensor inherits characteristics of gold including large surface area and high electrochemical conductivity, as well as high sensitivity and selectivity of aptamer toward its target, property of Arch-shape structure of Apt-CS conjugate to act as a gate and barrier for the access of redox probe to the surface of electrode and the function of Exo I as an enzyme which selectively digests the 3'-end of single stranded DNA (ssDNA). In the absence of streptomycin the gate remains closed. Thus, the electrochemical signal is weak. Upon addition of streptomycin, the Apt leaves the CS and binds to streptomycin and the Arch-shape structure is disassembled. Then, Exo I addition leads to a strong electrochemical signal. The designed electrochemical aptasensor exhibited high selectivity toward streptomycin with a limit of detection (LOD) as low as 11.4nM. Moreover, the developed electrochemical aptasensor was successfully used to detect streptomycin in milk and serum with LODs of 14.1 and 15.3nM, respectively.

Herein, a novel nanotherapeutic delivery platform was designed for subcellular co-delivery of α-PCNA aptamer as therapeutic aptamer and doxorubicin (Dox) as chemotherapy drug to tumor cells. Firstly, Dox was loaded onto the α-PCNA aptamer. Then, Dox-loaded α-PCNA was condensed by LAH4-L1 as a short cationic amphipathic peptide (LDPNs). Subsequently, the LDPNs was coated with AS1411 aptamer as targeting agent to obtain a therapeutic delivery system for tumor synergistic therapy. The results showed that the AS1411-modified LDPNs was stable in serum and could effectively accumulate at tumor site and be internalized into MCF-7 and 4T1 cells (target cells) through AS1411 and LAH4-L1. Also, the AS1411-modified LDPNs released its therapeutic agents in response to acidic conditions inside the cells. The superior anticancer activity of the AS1411-modified LDPNs compared to free Dox and other formulations was proved in 4T1 mouse breast cancer model. Overall, the results indicated that co-delivery of Dox and α-PCNA using AS1411 and LAH4-L1 can be used as a new approach to improve chemotherapy of breast cancer with less adverse effects and has great capacity for the clinical translation.

This study describes a novel electrochemical aptasensor for detection of α-synuclein (α-syn) oligomer, an important biomarker related to Parkinson's and Alzheimer's diseases. The sensing platform is based on exonuclease I (Exo I), terminal deoxynucleotidyl transferase (TdT) and methylene blue. The aptasensor exploits the improved sensitivity because of applications of TdT and Exo I and also a label-free aptamer (Apt). Furthermore, direct immobilization of complementary strand of aptamer (CS) instead of Apt on the surface of electrode prohibits Apt self-assembled monolayer aggregation and keeps the function of the Apt. In the absence of α-syn oligomer, TdT enhances lengths of Apt and CS and so, increases accumulation of methylene blue as redox agent on the surface of electrode, leading to a strong current signal. While in the presence of α-syn oligomer, Exo I digests CS on the electrode surface, resulting in less accumulation of methylene blue on the electrode surface and a weak current signal. The relative electrochemical signal of the aptasensor increased linearly with the logarithm of α-syn oligomer concentration in the range from 60 pM to 150 nM. The detection limit was 10 pM. Furthermore, the sensor showed high precision and repeatability for detection of α-syn oligomer in serum samples.

Zearalenone (ZEN) toxicity is a significant risk for human beings. Thus, it is of high importance to develop sensitive, precise, and inexpensive analytical methods for ZEN detection, especially in human serum. Here, a colorimetric aptasensor is presented for the determination of ZEN based on the nontarget-induced aptamer walker, catalytic reaction of gold nanoparticles (AuNPs), exonuclease III (Exo III) as a signal amplifier, and 4-nitrophenol as a colorimetric agent. Low amount of ZEN requirement and signal amplification are some of the distinct advantages of the proposed aptasensor. In the absence of ZEN, the aptamer (Apt) starts walking on the AuNP surface with the help of Exo III and binds to multiple complementary strands of aptamer, leading to the change of sample color from yellow to colorless. Upon the addition of ZEN, both the Apt and complementary strand exist as single-stranded DNAs on the surface of AuNPs, resulting in less access of 4-nitrophenol to the surface of AuNPs and less catalytic performance of AuNPs. In this situation, the color of the sample remains yellow (the color of 4-nitrophenol). The presented aptasensor was capable to detect ZEN in a wide linear dynamic range, 20-80 000 ng/L, with a detection limit of 10 ng/L. The prepared sensing strategy was successfully used for ZEN determination in the human serum sample.

Lead (Pb) is a serious environmental contaminant and one of the most toxic heavy metals. In this study a colorimetric aptasensor was designed for selective, sensitive and rapid detection of Pb2+, based on a triple-helix molecular switch (THMS) and peroxidase-like activity of gold nanoparticles (AuNPs). This sensor inherits the properties of THMS, including high stability and preserving the affinity and selectivity of the original aptamer and properties of peroxidase-like activity of AuNPs, such as fast readout and improvement of the sensitivity. In the absence of Pb2+, THMS is intact, leading to complete peroxidase-like activity of AuNPs and an obvious color change to purplish-blue. In the presence of Pb2+, the aptamer binds to Pb2+, the signal transduction probe (STP) leaves the THMS and adsorbs onto the surface of AuNPs, leading to inhibition of the peroxidase-like activity of AuNPs and no color change is observed. The designed aptasensor showed high selectivity toward Pb2+ with a limit of detection as low as 602 pM for Pb2+. The presented aptasensor was successfully used to detect Pb2+ in water and serum.

Digoxin is a useful drug in the treatment of heart failure. The therapeutic index of digoxin is very narrow. Thus, its detection in serum is of remarkable interest. In this study we designed a sensitive and selective fluorescent aptasensor for detection of digoxin based on silica nanoparticles (SNPs) coated with streptavidin. In the absence of digoxin, the fluorescence of the SNP–double stranded DNA (dsDNA) complex is strong. Upon addition of digoxin, the aptamer binds to its target, leading to release of the labeled-complementary strand from dsDNA and SNPs and decrease of the fluorescence intensity. This aptasensor showed a high selectivity toward digoxin and a limit of detection as low as 566 pM was obtained. This sensing platform is expected to be used successfully for detection of other drugs and biomolecules.

Digoxin is a cardiac glycoside with a narrow therapeutic index that is commonly used to treat heart failure. In this study, we designed selective, sensitive and fast fluorescence quenching and colorimetric aptasensors for the detection of digoxin based on aqueous gold nanoparticle (AuNP) suspension. In the absence of digoxin, aptamers are adsorbed on the surface of AuNPs. Therefore the well-dispersed AuNPs remain stable against salt-induced aggregation and the fluorescence of the ATTO 647N-aptamer is efficiently quenched by AuNPs. In the presence of digoxin, aptamers bind to digoxin, leading to the aggregation of AuNPs by salt, resulting in a color change from red to blue and recovery of the fluorescence emission. Fluorescence quenching and colorimetric aptasensors showed high selectivity toward digoxin with a limit of detection (LOD) as low as 392 and 571 pM, respectively. Our designed aptasensors were successfully used to detect digoxin in serum.

The authors describe a method for the colorimetric determination of the pesticide malathion. It is based on the use of a hairpin structure consisting of a complementary strand of aptamer and a double-stranded DNA (dsDNA) structure to protect gold nanoparticles (AuNPs) against salt-induced aggregation. In the absence of malathion, the dsDNA structure is preserved on the surface of AuNPs and the color of the AuNPs in solutions containing NaCl remains red. However, in the presence of malathion, a hairpin structure of complementary strand is formed. The Aptamer/Malathion complex and the complementary strand are released from the surface of the AuNPs. As a result, the AuNPs undergo salt-induced aggregation which is accompanied by a color change to blue. The assay allows malathion to be quantified within 35 min (A650/A520 was measured). The detection limit is 1 pM, and response is linear in the 5 pM to 10 nM malathion concentration range. The method is specific and was successfully applied to the determination of malathion in spiked human serum samples.

Insulin plays an important role in glucose metabolism and its detection in biological fluids is of interest. In this study, a triple-helix molecular switch was employed for the simple, sensitive, and rapid determination of insulin. The triple-helix molecular switch was composed of a target specific aptamer sequence flanked by two arm segments and a dual-labeled oligonucleotide acting as a signal transduction probe. This approach takes advantage of unique properties of aptamers and triple-helix molecular switches such as high affinity, selectivity, and stability. In the absence of insulin, the fluorescence of triple-helix molecular switch is on. Upon addition of insulin, the aptamer binds to its target, leading to the release of the signal transduction probe, folding of the signal transduction probe to a stem loop structure, and the quenching of the fluorescence. This sensor showed a high selectivity toward insulin and a limit of detection as low as 9.97 nM. The sensor was employed for the determination of...

Lead contamination is a serious environmental problem with toxic effects in human. Here, we developed a simple and sensitive sensing method employing ATTO 647N/aptamer-SWNT ensemble for detection of Pb(2+). This method is based on the super quenching capability of single-walled carbon nanotubes (SWNTs), high affinity of the aptamer toward Pb(2+) and different propensities of ATTO 647N-aptamer and ATTO 647N-aptamer/Pb(2+) complex for adsorption on SWNTs. In the absence of Pb(2+), the fluorescence of ATTO 647N-aptamer is efficiently quenched by SWNTs. Upon addition of Pb(2+), the aptamer binds to its target, leading to the formation of a G-quadruplex/Pb(2+) complex and does not interact with SWNTs and ATTO 647N-aptamer starts fluorescing. This sensor exhibited a high selectivity toward Pb(2+) and a limit of detection (LOD) as low as 0.42 nM was obtained. Also this sensor could be applied for detection of Pb(2+) ions in tap water and biological sample like serum with high sensitivity.

There is a prompt need for determination of aflatoxin B

Cytokines play a key role in the pathogenesis of coronary artery disease (CAD). The aim of current study was to investigate the relationship between the serum concentrations of 12 cytokines with mortality and extent of CAD in individuals undergoing angiography and healthy controls. 342 CAD patients were recruited and divided into 2 groups: those with ≥50% occlusion in at least one coronary artery [Angiography (+)] or 2.16 pg/mL IL-6 had a > 94% sensitivity and 70% specificity in predicting 2 years mortality in the subjects with a serum MCP-1 > 61.95 pg/ mL, and patients having IL-6/MCP-1 combination had a shorter survival.Our findings demonstrate that CAD patients with serum MCP-1 and IL-6 levels of >61.95 and >2.16 pg/mL had a higher mortality with 94.1% sensitivity and 70.5% specificity for predicting mortality in CAD patients.

Monitoring of myoglobin (Mb) in human blood serum is highly in demand for early diagnosis of acute myocardial infarction (AMI). Here, a novel electrochemical aptasensor was developed for ultrasensitive and selective detection of Mb, based on Y-shape structure of dual-aptamer (DApt)-complementary strand of aptamer (CS) conjugate, gold electrode and exonuclease I (Exo I). The designed aptasensor obtains features of gold, such as high electrochemical conductivity and large surface area, property of Y-shape structure of DApt-CS conjugate to function as a gate and obstacle for the access of redox probe to the surface of electrode, as well as high specificity and sensitivity of aptamer toward its target and Exo I as an enzyme which specifically degrades the 3'-end of single-stranded DNA (ssDNA). In the absence of Mb, the Y-shape structure remains intact. So, a weak electrochemical signal is observed. Upon addition of target, the DApt leave the CS and bind to Mb, leading to disassembly of Y-shape structure and following the addition of Exo I, a strong electrochemical signal could be recorded. The fabricated aptasensor showed high selectivity toward Mb with a limit of detection (LOD) as low as 27 pM. Besides, the developed aptasensor was effectively applied to detect Mb in human serum.

Cocaine is one of the most commonly misused stimulant which could influence the central nervous system. In this study, a fluorescent aptamer-based sensor (aptasensor) was designed for sensitive and selective detection of cocaine, based on hairpin structure of complementary strand of aptamer (CS), target-induced release of aptamer (Apt) from CS and two kinds of nanoparticles, including silica nanoparticles (SNPs) coated with streptavidin and gold nanoparticles (AuNPs). The designed aptasensor acquires characteristics of AuNPs such as unique optical properties and large surface area, SNPs as amplifiers of fluorescence intensity, higher affinity of Apt toward its target relative to its CS, and finally the hairpin structure of CS that brings the fluorophore (FAM) to close proximity to the surface of SNPs. In the absence of cocaine, FAM is in close proximity to the surface of AuNPs, resulting in a weak fluorescence emission. In the presence of target, FAM comes to close proximity to the surface of SNPs because of the formation of hairpin structure of CS, leading to a very strong fluorescence emission. The fabricated fluorescent aptasensor exhibited a good selectivity toward cocaine with a limit of detection (LOD) as low as 209 pM. Moreover, the designed aptasensor was successfully utilized to detect cocaine in serum with a LOD as low as 293 pM.

Cocaine is a strong central nervous system stimulant and one of the most commonly abused drugs. In this study, an electrochemical aptasensor was designed for sensitive and selective detection of cocaine, based on single-walled carbon nanotubes (SWNTs), gold electrode and complimentary strand of aptamer (CS). This electrochemical aptasensor inherits properties of SWNTs and gold such as large surface area and high electrochemical conductivity, as well as high affinity and selectivity of aptamer toward its target and the stronger interaction of SWNTs with single-stranded DNA (ssDNA) than double-stranded DNA (dsDNA). In the absence of cocaine, a little amount of SWNTs bind to Aptamer-CS-modified electrode, so that the electrochemical signal is weak. In the presence of cocaine, aptamer binds to cocaine, leaves the surface of electrode. So that, a large amount of SWNTs bind to CS-modified electrode, generating to a strong electrochemical signal. The designed electrochemical aptasensor showed good selectivity toward cocaine with a limit of detection (LOD) as low as 105 pM. Moreover, the fabricated electrochemical aptasensor was successfully applied to detect cocaine in serum with a LOD as low as 136 pM.

Antibiotic residues in animal foodstuffs are of great concern to consumers. In this study, fluorescence quenching and colorimetric aptasensors were designed for detection of streptomycin based on aqueous gold nanoparticles (AuNPs) and double-stranded DNA (dsDNA). In the absence of streptomycin, aptamer/FAM-labeled complementary strand dsDNA is stable, resulting in the aggregation of AuNPs by salt and an obvious color change from red to blue and strong emission of fluorescence. In the presence of streptomycin, aptamer binds to its target and FAM-labeled complementary strand adsorbs on the surface of AuNPs. So the well-dispersed AuNPs remain stable against salt-induced aggregation with a wine-red color and the fluorescence of FAM-labeled complimentary strand is efficiently quenched by AuNPs. The colorimetric and fluorescence quenching aptasensors showed excellent selectivity toward streptomycin with limit of detections as low as 73.1 and 47.6 nM, respectively. The presented aptasensors were successfully used to detect streptomycin in milk and serum.

Clinical administrations of anthracyclines are limited by cardiotoxicity and myelosuppression. Targeted delivery of anticancer agents is especially important in reducing their side effects. In this work, A10 (Apt), an aptamer for prostate-specific membrane anytigen (PSMA), was applied for targeted delivery of Epirubicin (Epi) to LNCaP cells (PSMA+). Flow cytometry analysis showed that PEG-Apt-Epi complex was internalized effectively to LNCaP cells (PSMA+), but not to PC3 cells (PSMA−). This fact was confirmed by less cytotoxicity of PEG-Apt-Epi complex in PC3 cells in comparison with Epi alone. No significant change in viability between Epi- and complex-treated LNCaP cells was observed. In conclusion, PEG-Apt-Epi complex is an efficient and simple system for specific delivery of drug to PSMA-expressing cell lines.