Developing Aptamer-Based Colorimetric Opioid Tests

Opioids collectively cause over 80,000 deaths in the United States annually. The ability to rapidly identify these compounds in seized drug samples on-site will be essential for curtailing trafficking and distribution. Chemical reagent-based tests are fast and simple but also notorious for giving false results due to poor specificity, whereas portable Raman spectrometers have excellent selectivity but often face interference challenges with impure drug samples. In this work, we develop on-site sensors for morphine and structurally related opioid compounds based on in vitro-selected oligonucleotide affinity reagents known as aptamers. We employ a parallel-and-serial selection strategy to isolate aptamers that recognize heroin, morphine, codeine, hydrocodone, and hydromorphone, along with a toggle-selection approach to isolate aptamers that bind oxycodone and oxymorphone. We then utilize a new high-throughput sequencing-based approach to examine aptamer growth patterns over the course of selection and a high-throughput exonuclease-based screening assay to identify optimal aptamer candidates. Finally, we use two high-performance aptamers with KD of ∼1 μM to develop colorimetric dye-displacement assays that can specifically detect opioids like heroin and oxycodone at concentrations as low as 0.5 μM with a linear range of 0-16 μM. Importantly, our assays can detect opioids in complex chemical matrices, including pharmaceutical tablets and drug mixtures; in contrast, the conventional Marquis test completely fails in this context. These aptamer-based colorimetric assays enable the naked-eye identification of specific opioids within seconds and will play an important role in combatting opioid abuse.

Suite of Aptamer-Based Sensors for the Detection of Fentanyl and Its Analogues

Fentanyl and its analogues are potent synthetic opioids that are commonly abused and are currently the number one cause of drug overdose death in the United States. The ability to detect fentanyl with simple, rapid, and low-cost tools is crucial for forensics, medical care, and public safety. Conventional on-site testing options for fentanyl detection─including chemical spot tests, lateral-flow immunoassays, and portable Raman spectrometers─each have their own unique flaws that limit their analytical utility. Here, we have developed a series of new aptamer-based assays and sensors that can detect fentanyl as well as several of its analogues in a reliable, accurate, rapid, and economic manner. These include colorimetric, fluorescent, and electrochemical sensors, which can detect and quantify minute quantities of fentanyl and many of its analogues with no response to other illicit drugs, cutting agents, or adulterants─even in interferent-ridden binary mixtures containing as little as 1% fentanyl. Given the high performance of these novel analytical tools, we foresee the potential for routine use by medical and law enforcement personnel as well as the general public to aid in rapid and accurate fentanyl identification.

An increase in DNA G-quadruplex formation in acute myelocytic leukemia is detected by a supramolecular probe

Acute myeloid leukemia (AML) is a common acute leukemia in both adults and children, with poor early detection and diagnosis. Therefore, identifying new indicators for AML detection is significant for effective treatment. Here, we developed a supramolecular probe that exhibits high specificity and sensitivity to G-quadruplex structures in physiological buffer solution, chromosomes, and cells. Using this probe, we tested the DNA extracted from different types of cells and found that the DNA extracted from human acute myeloid leukemia cells HL-60 and KG-1 enhanced the probe fluorescence more significantly than the DNA extracted from other cells. This phenomenon may be related to a large number of G-quadruplexes in acute myeloid leukemia cells, implicating that G-quadruplex levels may be a potential indicator for the detection of acute myeloid leukemia.

DNA Aptamer-Cyanine Complexes as Generic Colorimetric Small-Molecule Sensors

Aptamers are promising biorecognition elements for sensors. However, aptamer-based assays often lack the requisite levels of sensitivity and/or selectivity because they typically employ structure-switching aptamers with attenuated affinity and/or utilize reporters that require aptamer labeling or which are susceptible to false positives. Dye-displacement assays offer a label-free, sensitive means for overcoming these issues, wherein target binding liberates a dye that is complexed with the aptamer, producing an optical readout. However, broad utilization of these assays has been limited. Here, we demonstrate a rational approach to develop colorimetric cyanine dye-displacement assays that can be broadly applied to DNA aptamers regardless of their structure, sequence, affinity, or the physicochemical properties of their targets. Our approach should accelerate the development of mix-and-measure assays that could be applied for diverse analytical applications.

Highly Selective Detection of K+ Based on a Dimerized G-Quadruplex DNAzyme

Potassium ion (K⁺) plays a crucial role in biological systems, such as maintaining cellular processes and causing diseases. However, specifically, the detection of K⁺ is extremely challenging because of the coexistence of the chemically similar ion of Na⁺ under physiological conditions. In this work, a K⁺ specific biosensor is constructed on the basis of a dimerized G-quadruplex (GQ) DNA, which is promoted by K⁺, and the enzymatic activity of the resulting DNAzyme depends on the concentration of the K⁺. The K⁺ in a 1-200 mM concentration range can be selectively detected by visual color, UV-Vis absorbance or fluorescence even if the concentration of the accompanying Na⁺ is up to 140 mM at an ambient condition up to 45 °C. In addition, this system can also be used to selectively detect NH₄⁺ in a 5-200 mM concentration range. This dimerized DNAzyme offers a new type of biosensor with a potential application in the biological system.

Direct detection of potassium and lead (II) ions based on assembly-disassembly of a chiral cyanine dye /TBA complex

A highly selective and sensitive direct detection of potassium (K⁺) and lead (Pb²⁺) ions was developed by using the assembly and disassembly of a chiral cyanine dye/TBA complex. The dye DMSB (3-ethyl-2-[3-(3-ethyl-3H-benzoselenazol-2-ylidene)-2-methylprop-1-enyl] benzoselenazolium bromide) loses the ability of self-assembly, but it can be activated by thrombin-binding aptamer (TBA) G-quadruplex structure. And only the TBA G-quadruplex formed in the presence of K⁺, can strongly induce J-aggregate signals of DMSB. Because the Pb²⁺ ions can bind and stabilize the TBA G-quadruplex with much higher efficiency than K⁺, the J-aggregate signals of DMSB falls sharply when the Pb²⁺ is present. As a result, the assembly and disassembly of DMSB allows the selective detection of 10 μM K⁺ and 20 nM Pb²⁺ respectively, even the competitive sodium ion (Na⁺) was as high as 145 mM. The linear correlation existed between the J-aggregate intensity and the concentration of K⁺ and Pb²⁺ over the range of 0.5-5.0 mM and 200-2000 nM, respectively. Moreover, the concentration of K⁺ (∼3 mM) and Pb²⁺ (below 20 nM) in human blood serum samples were determined by the present method, which agreed well with inductively coupled plasma mass spectrometry (ICP-MS). This work not only opens a door for the further development of G-quadruplex-based aptasensor in complex real system, but also provides a simple and versatile sensing platform for ion detection in clinic.

Visualized detection of apo-transferrin based on cyanine dye supramolecular assembly

In this work, a new biological probe for human transferrin (hTf) detection based on a cyanine dye ETC supramolecular assembly was designed. In sub-micromolar level, apo-hTf could induced the ETC aggregations transferred from H-aggregations to J-band with color change from pink to blue, while holo-hTf hardly possessed the ability, indicating ETC could specifically identify apo-hTf. The present study allowed for apo-hTf detection in the range of 8-80 nM with a detection limit of 2.8 nM and the sensitivity of visualization was around 70 nM. To further examine the suitability, iron ions were added into apo-hTf to stimulate the transformation from open conformation to the closed one gradually. It has been confirmed through tryptophan internal fluorescence quenching and the decrease of ETC J-aggregation. The interaction between ETC and apo-hTf performed high affinity that K_a was reached to 10⁶ M^-1 with a high selectivity. The potential in practical applications of this method has been tested for detection apo-hTf in human serum.

Electrochemical aptasensor based on a potassium ion-triggered DNA conformation transition and self-assembly on an electrode

A sensitive and selective electrochemical aptasensor was developed for the detection of potassium ions based on a simple sensing principle and straightforward operation.

Reversible regulation of the supramolecular chirality of a cyanine dye by using the G-quadruplex structure as a template

Multiple cycle regulation of the supramolecular chirality of a cyanine dye has been successfully achieved by using DNA G-quadruplexes as templates, which is easily controllable by repeated addition of Ag(+) and cysteine (Cys). This work provides an easy and controllable strategy for the chiral regulation of supramolecules.

Novel fluorescent cationic benzothiazole dye that responds to G-quadruplex aptamer as a novel K+ sensor

A fluorescent cationic benzothiazole dye that selectively targets a G-quadruplex aptamer was designed and synthesized as a K⁺ sensor.

A label-free fluorescence assay for potassium ions using riboflavin as a G-quadruplex ligand

A label-free fluorescence K⁺assay was developed using riboflavin, a new G-quadruplex ligand, and a G-quadruplex sequence (PW17).

Versatile G-quadruplex-mediated strategies in label-free biosensors and logic systems

This review addresses how G-quadruplex (G4)-mediated biosensors convert the events of target recognition into a measurable physical signal. The application of label-free G4-strategies in the construction of logic systems is also discussed.

A supramolecular probe for colorimetric detection of Pb2+ based on recognition of G-quadruplex

A colorimetric probe of Pb²⁺ has been designed based on the mechanism that a supramolecular probe selectively recognized the Pb²⁺-induced conformational transition of G-quadruplexes.

Visual detection of mercury(ii) based on recognition of the G-quadruplex conformational transition by a cyanine dye supramolecule

Visual detection of mercury(ii) based on recognition of the G-quadruplex conformational transition by a cyanine dye supramolecule is reported.

Microflow injection potassium bioassay based on G-quadruplex DNAzyme-enhanced chemiluminescence

By taking advantage of microflow injection chemiluminescence analysis, we developed a distinctive microfluidic bioassay method based on G-Quadruplex DNAzyme-enhanced chemiluminescence for the determination of K(+) in human serum. AGRO100, the G-rich oligonucleotide with high hemin binding affinity was primarily selected as a K(+) recognition element. In the presence of K(+), AGRO100 folded into G-quadruplex and bound hemin to form DNAzyme, which catalyzed the oxidation of luminol by H2 O2 to produce chemiluminescence. The intensity of chemiluminescence increased with the K(+) concentration. In the study, the DNAzyme showed both long-term stability and high catalytic activity; other common cations at their physiological concentration did not cause notable interference. With only 6.7 × 10(-13) mol of AGRO100 consumption per sample, a linear response of K(+) ranged from 1 to 300 µmol/L, the concentration detection limit 0.69 µmol/L (S/N = 3) and the absolute detection limit 1.38 × 10(-12) mol were obtained. The precision of 10 replicate measurements of 60 µmol/L K(+) was found to be 1.72% (relative standard deviation). The accuracy of the method was demonstrated by analyzing real human serum samples.