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Herein, a facile fluorescent CRISPR-Cas12a-based sensing strategy is presented for prostate specific antigen (PSA), as a prostate cancer biomarker, with the assistance of a cruciform DNA nanostructure and PicoGreen (PG) as a fluorochrome. Highly sensitive recognition of PSA is one of the virtues of the proposed method which comes from the use of unique features of both CRISPR-Cas12a and DNA structure in the design of the aptasensor. The presence of PSA creates a cruciform DNA nanostructure in the sample which can be loaded by PG and make sharp fluorescence emission. While, when there is no PSA, the CRISPR-Cas12a digests sequences 1 and 3 as single-stranded DNAs, causing no DNA structure and a negligible fluorescence is detected after addition of PG. This aptasensor presents a sensitive recognition performance with detection limit of 4 pg/mL and a practical use for determination of PSA in serum samples. So, this analytical strategy introduces a convenient and highly sensitive approach for detection of disease biomarkers.

Developed herein is an aptasensing array based on liquid crystal (LC) for monitoring of tobramycin (TOB) antibiotic. The direction of LC molecules from vertical to a random status was induced by the conformational changes of the specific aptamer due to its selective interaction with the target. The dark view of the aptasensing platform changed to colorful through observation by a polarized light microscope that clarifies the TOB presence. The aptasensor is especially able to determine TOB in the linear concentration range of 0.005-600 pM with a limit of detection (LOD) as 0.0021 pM. The TOB values can be determined successfully in the milk and chicken egg samples that highlights the potential applicability of the designed aptasensor. The proposed sensing approach is facile, operator-independent, label-free, and ultra-sensitive, making it novel for developing real-time portable sensing devices for future.

Herein, a simple electrochemical sensor is proposed for 17β-estradiol (E2) determination. In this sensing platform, split DNA aptamers for E2 were applied as recognizing agents. In the presence of E2, split aptamers are bound to E2 and establish split1-E2-split2 complex as a bridge on the surface of electrode. This physical bar leads to ultrasensitive detection of E2. This aptasensor is capable of recognizing E2 within 30 min without complicated procedures and expensive equipment. This sensing approach indicated a wide linear range with detection limits of 0.5 pM and 0.7 pM for E2 in tap water and milk samples, respectively. Simplicity and high specificity of the proposed electrochemical aptasensor make it an ideal sensing platform for ultra-low detection of other targets in complicated samples by replacement of split DNA aptamers.

Colorimetric approaches have received noticeable attention among sensing methods in view of simplicity and watching the color change of sample by the naked eyes. However, developing colorimetric sensing methods which show high sensitivity is still problematic. Herein, based on CRISPR-Cas12a, rolling circle amplification (RCA) and catalytic activity of gold nanoparticles (AuNPs), a colorimetric aptasensor was introduced for highly sensitive detection of aflatoxin M

In this study, a fluorescent aptasensor is described for ultrasensitive detection of prostate-specific antigen (PSA) using DNA triangular prism as a platform for attachment of fluorophore (PicoGreen, PG), streptavidin magnetic beads (SMBs) and RecJf exonuclease as enhancers of fluorescence difference between presence and absence of target. Presence of PSA leads to the formation of the DNA origami. So, a strong fluorescence is observed following the addition of PG. while, the DNA triangular prism cannot be formed in the lack of target. Thus, a very weak fluorescence can be measured after addition of PG. The proposed biosensor indicated high selectivity, a broad linear range from 200 pg/mL to 300 ng/mL and a very low detection limit of 30 pg/mL for PSA. Applying the designed aptasensor, PSA was successfully detected in human serum samples. This work provides a new way for detection of biomarkers in clinical samples.

Kanamycin is an aminoglycoside antibiotic that can be useful against both gram negative and positive bacteria. However, if its serum levels are not controlled properly, it can cause serious side effects like ototoxicity and nephrotoxicity. The aim of this study was to design a simple and rapid fluorescent aptasensor for detection of kanamycin, based on Aptamer/Complementary strand (dsDNA)-capped mesoporous silica nanoparticles (MSNs) and Rhodamine B as a fluorescent probe. The MSNs pores were filled with Rhodamine B and then gated with dsDNA. In the presence of kanamycin, the aptamer sequence was separated from its complementary strand (CS), so that, uncovered the pores and leading to leakage of Rhodamine B. Thus, a significant increase in the fluorescence intensity was observed. The relative fluorescence intensity showed a linearity range from 24.75 nM to 137.15 nM of kanamycin with a detection limit of 7.5 nM. The aptasensor also showed to be useful for detection of kanamycin in serum samples and was able to distinguish kanamycin from other antibiotics, resulting in a sensitive, rapid and inexpensive method for kanamycin detection.

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%.

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.

It is great significance to identify interferon-gamma (IFN-γ), as a biological marker for diagnosis of latent tuberculosis, in serum samples. In this paper, a novel fluorescent aptasensor was fabricated and applied for sensitive and specific detection of IFN-γ. This biosensor was based on hairpin structure of oligonucleotide, single-stranded DNA-binding protein (SSB), copper nanoparticles (CuNPs) and silica nanoparticles coated with streptavidin (SNPs-Streptavidin). The presences of double-stranded DNA (dsDNA) region and poly thymine (T) in the hairpin structure of the oligonucleotide, SSB and SNPs-streptavidin caused IFN-γ determination with high selectivity and sensitivity. Upon addition of IFN-γ, the hairpin structure of the oligonucleotide was disassembled and therefore, poly T strand interacted with SSB and a weak fluorescence signal was obtained. Without introduction of IFN-γ, the hairpin structure of oligonucleotide was preserved and fluorescent CuNPs were formed on the stem region of hairpin structure of oligonucleotide, resulting in strong fluorescence intensity. Under optimal conditions, concentration as low as 1 pg/mL IFN-γ could be detected, with a linear range between 10 pg/mL and 4 ng/mL. The presented method was further performed for detection of IFN-γ in the spiked human serum samples and the recoveries were 92.52%–98.32%, showing the great potential of the proposed analytical method in biomedical analysis.