Selective Detection Of Small Molecules Research Articles

Fluorescence Label‐Free Doxorubicin Sensor Using Polystyrene Sulfonate as a Synthetic Receptor in Whispering Gallery Mode Microresonators

AbstractThe conventional quantification of Doxorubicin (DXR), a crucial anticancer drug, typically relies on complex and expensive techniques, limiting measurements beyond hospital settings and at different time intervals. Here, a label‐free fluorescence sensor is presented for DXR utilizing Whispering Gallery Mode (WGM) resonators. The resonators are based on fluorescent microparticles coated with a nanometer‐thick polystyrene sulfonate (PSS) layer serving as a synthetic receptor. The sensor demonstrates linear response for both position and width of the resonance peaks within the concentration range of 1–10 µg mL−1 of DXR of clinical interest. It also exhibits good selectivity against other chemotherapy drugs and can operate in complex biological fluids. The findings underscore the potential of WGM resonators as versatile multiparameter sensors for the sensitive and selective detection of small molecules, also in complex biological media.

Antibody-Bridged DNAzyme Walker for Sensitive Detection of Small Molecules.

Sensitive detection of small molecules with biological and environmental interests is important for many applications, such as food safety, disease diagnosis, and environmental monitoring. Herein, we propose a highly selective antibody-bridged DNAzyme walker to sensitively detect small molecules. The antibody-bridged DNAzyme walker consists of a track, small-molecule-labeled DNAzyme walking strand, and antibody against small molecules. The track is built by co-modifying fluorophore-labeled substrates and small-molecule-labeled DNA linkers onto a gold nanoparticle (AuNP). In the absence of the target molecule, the antibody binds small molecule labels at the DNAzyme walking strand and the DNA linker, driving the DNAzyme walking strand on the surface of the AuNP. The attached DNAzyme walking strand moves along the track and cleaves substrates to generate high fluorescence signals to achieve signal amplification. As target molecules exist, they competitively bind with antibody to displace the small-molecule-labeled linker and DNAzyme walking strand, rendering the DNAzyme walker inactive in substrate cleavage and causing weak fluorescence. By using this antibody-bridged DNAzyme walker, we achieved sensitive detection of two biologically important small molecules, digoxin and folic acid. This work provides a new paradigm by combining the signal amplification strategy of a DNA walker and immunorecognition for sensitive and selective detection of small molecules.

Rational Truncation of Aptamer for Ultrasensitive Aptasensing of Chloramphenicol: Studies Using Bio-Layer Interferometry.

Aptamers are an excellent choice for the selective detection of small molecules. However, the previously reported aptamer for chloramphenicol suffers from low affinity, probably as a result of steric hindrance due to its bulky nature (80 nucleotides) leading to lower sensitivity in analytical assays. The present work was aimed at improving this binding affinity by truncating the aptamer without compromising its stability and three-dimensional folding. Shorter aptamer sequences were designed by systematically removing bases from each or both ends of the original aptamer. Thermodynamic factors were evaluated computationally to provide insight into the stability and folding patterns of the modified aptamers. Binding affinities were evaluated using bio-layer interferometry. Among the eleven sequences generated, one aptamer was selected based on its low dissociation constant, length, and regression of model fitting with association and dissociation curves. The dissociation constant could be lowered by 86.93% by truncating 30 bases from the 3' end of the previously reported aptamer. The selected aptamer was used for the detection of chloramphenicol in honey samples, based on a visible color change upon the aggregation of gold nanospheres caused by aptamer desorption. The detection limit could be reduced 32.87 times (1.673 pg mL-1) using the modified length aptamer, indicating its improved affinity as well as its suitability in real-sample analysis for the ultrasensitive detection of chloramphenicol.

Multicomponent Anti-Kasha’s Rule Emission from Nanotubular Metal–Organic Frameworks for Selective Detection of Small Molecules

The peak photoluminescence (PL) of conventional fluorophores is independent of the excitation wavelength (called Kasha's rule), while the search of metal-organic framework materials with the so-called anti-Kasha's rule emission remains very limited. Herein, we report the observation of anti-Kasha's rule emission in a multicomponent PL three-dimensional nanotubular metal-organic framework (abbr. MOF-NT), [Zn(μ-L)(μ-bix)]n·0.33nH2O [H2L = biphenyl-3,5-dicarboxylic acid; bix = 1,4-bis(imidazole-1-ylmethyl)benzene]. The MOF-NT crystalline sample represents a notable example of strong excitation-dependent fluorescence from the ultraviolet to the visible spectral region. Moreover, by virtue of electronic flexibility and high PL efficiency, MOF-NT shows a discriminative PL response between isomeric nitroaromatic compounds. The work demonstrated the intrinsic anti-Kasha's rule emission in the crystalline-state MOF materials, providing new visions for the development of advanced solid-state emissive materials.

Bifunctional ligand-mediated amplification of polydiacetylene response to biorecognition of diethylstilbestrol for on-site smartphone detection

Polydiacetylene (PDA) is very suited for sensitively detecting large biomolecules, and its unique chromatic properties enable visual read-out. However, application to the selective detection of small molecules remains challenging. Here, bifunctional ligands are studied to amplify the color change of PDA for biorecognition of small molecules for the smartphone-based detection of diethylstilbestrol (DES). PDA is decorated with streptavidin (PDA-SA, blue), and biotin-modified DES (bio-DES) is prepared as a bifunctional ligand to couple with PDA-SA and DES antibody. Since multiple bio-DES can bind to a single SA, then multiple SAs on PDA lead to an increased surface coverage of the vesicle. In samples without DES, PDA-SA-bio-DES-DES antibody complexes will form, leading to a color transition (blue to red); this color transition is greatly amplified by antibody-induced aggregation of the complexes. When DES is present, aggregation is inhibited due to competition for the antibody and PDA-SA-bio-DES retains its blue color. A linear relationship (0.4–1250 ng mL−1) is found between the colorimetric response and the logarithmic DES concentration, with adequate selectivity, accuracy (82.24–118.64%), and precision (below 8.24%). Finally, a paper-based DES PDA biosensor is developed with visual and smartphone-based detection limits of 10 ng mL−1 and 0.85 ng mL−1 in water, respectively.

In Situ Electrodeposition of Gold Nanostructures in 3D Ultra‐Thin Hydrogel Skins for Direct Molecular Detection in Complex Mixtures with High Sensitivity

AbstractSurface‐enhanced Raman spectroscopy (SERS) based on nanostructured metals has promise as a nondestructive tool for sensitive molecular detection. However, metal surfaces are prone to fouling by the nonspecific adsorption of macromolecules, which limits the selective detection of small molecules in complex fluids. Therefore, samples must be purified and enriched before Raman analysis, which makes on‐site detection difficult. In the present work, Au nanopillar arrays are encapsulated with ultra‐thin hydrogel skins to protect the metal surfaces against macromolecular interferents while selectively allowing the infusion of small target molecules. In addition, densely packed Au nanostructures are produced in situ in the 3D mesh of the hydrogel skin via electrodeposition, which effectively captures targets into dense plasmonic nanogaps, providing rapid and ultrasensitive molecular detection. The synergistic influence of the size‐selective permeability of the hydrogel skin and the in situ formation of hotspots enables the direct, highly sensitive detection of pyocyanin dissolved in an aqueous solution of bovine serum albumin and human serum. It is believed that the new nanocomposite materials and techniques will enable rapid and affordable SERS‐based on‐site analysis and point‐of‐care testing.

A ligation-triggered and protein-assisted fluorescence anisotropy amplification platform for sensitive and selective detection of small molecules in a biological matrix.

Effective detection of biomolecules is important for biological research and medical diagnosis. We here propose a ligation-triggered and protein-assisted fluorescence anisotropy amplification platform for sensitive and selective detection of small biomolecules in a complex biological matrix. In the proposed method, in the presence of target small molecules, FAM-labeled DNA 1 and biotin-labeled DNA2 were ligated to produce an integrated DNA. As a result, taking advantage of the extraordinary strong interaction between biotin and streptavidin, we employed a novel mass amplification strategy for sensitive detection of small molecules through fluorescence anisotropy. The method could detect ATP from 0.05 to 1 μM, with a detection limit of 41 nM, and detect NAD+ from 0.01 to 1 μM, with a detection limit of 6.7 nM. Furthermore, ligase-specific dependence of different cofactors provides good selectivity for the detection platform. As a result, the new platform has a broad spectrum of applications both in bioanalysis and biomedical fields.

Tailoring the surface chemistry of SiO2-based monoliths to enhance the selectivity of SALDI-MS analysis of small molecules

Due to their 3D geometry, surface chemistry, high porosity and large surface area, SiO2-based monoliths were explored as novel surface-assisted laser desorption/ionization-mass spectrometry (SALDI-MS) substrates for the sensitive and selective detection of small molecules of varying polarities. For this purpose, the surface of a hydrophilic SiO2 monolith was functionalized with moderately hydrophobic C-8 and more hydrophobic C-18 groups to form C8-SiO2 and C18-SiO2 monoliths, respectively. These monoliths were characterized using N2 adsorption-desorption, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). All of the monoliths displayed V isotherms and H1-type hysteresis loops, and they had surface areas of no less than 400 m2 g−1. The presence of bands at 2853 and 2927 cm−1 in the FTIR spectra of the respective C8-SiO2 and C18-SiO2 monoliths demonstrated that they contained alkyl chains on their surfaces. A proof-of-concept study was conducted to assess the ability of the SiO2-based monoliths to serve as substrates for SALDI-MS analysis of small molecules, including hydrophilic vitamin C, moderately hydrophobic caffeine and hydrophobic carbazole. When the hydrophilic SiO2 monolith was used as the SALDI substrate, the spectrum of vitamin C showed a large molecular ion signal, while that of carbazole exhibited only an insignificant ion signal. By contrast, the use of the hydrophobic monolith C18-SiO2 led to a high intensity molecular ion signal in the SALDI spectrum of nonpolar carbazole, while the spectrum of vitamin C showed a minimal ion signal. The observed selectivities appear to be a consequence of strong interactions occurring between the substrates and analytes of matching polarities that prevent early laser irradiation-induced analyte desorption. Furthermore, the studies showed that the more hydrophobic monolith C18-SiO2 displayed higher selectivity toward enhancing the SALDI signal of the longer chain fatty acid arachidic acid (C20), while the hydrophilic SiO2 monolith was highly selective in promoting shorter chain myristic acid (C14). In addition, the feasibility of using the C18-SiO2 monolith for SALDI detection of the hydrophobic antidepressant drugs desipramine and trimipramine in carbonated malt beverages was also evaluated. The results showed that this monolith enabled the detection of the protonated forms of these drugs, with respective limits of detection (LODs) of 10 µg mL−1 and 1 ng mL−1. This proof-of-principle study demonstrates that SiO2-based monoliths are potentially important SALDI substrates for the selective enhancement of SALDI signals of a vast range of small molecule analytes.

Analyte induced AuNPs aggregation enhanced surface plasmon resonance for sensitive detection of paraquat

Paraquat (PQ) residue is harmful for people's health. This work fabricated an efficient approach to determine PQ sensitively. We exploited a novel surface plasmon resonance (SPR) detection system based on the analyte induced network architecture of supermolecules modified gold nanoparticles (AuNPs) on the chip surface. para-Sulfonatocalix[4]arene (pSC4) were used as a recognition molecule for paraquat. PQ can mediate the aggregation of pSC4 capped AuNPs (pSC4-AuNPs) through the host-guest recognition, which can be used as signal amplification for PQ assay. This achievement is due to several outstanding properties of this detection system: first, local SPR and high refractive index of AuNPs can enhance the signal of SPR dramatically; second, AuNPs is more stable and biocompatible and diffusely used in colorimetric methods; third, the network AuNPs structure has unique photo characterization for enhancement of SPR. Analyte induced AuNPs aggregation amplified SPR assay shows dramatic signal enhancement ability. The detection limit for PQ was found to be 2.2 pM This strategy provides a new concept for developing sensitive SPR sensors for the highly selective detection of small molecules.

Designer SiO2@Au nanoshells towards sensitive and selective detection of small molecules in laser desorption ionization mass spectrometry

We report a novel platform using optimized SiO2@Au core–shell structures as matrices for highly efficient laser desorption/ionization mass spectrometry analysis of small biomolecules (MW<700Da). Owing to the designer structure, SiO2@Au nanoshells can achieve low detection-of-limits (~pmol–fmol) in mass spectrometry and selective laser desorption/ionization in bio-mixtures towards diverse small molecules. By further surface modification with aptamers, Apt-SiO2@Au nanoshells allowed simultaneously targeted enrichment and detection of kanamycin with a detection limit at 200pM. Our work not only starts new applications of SiO2@Au nanoshells in mass spectrometry, but also contributes to advanced analysis of either a group of small molecules or one target small molecule from complex bio-samples in a pre-designed manner for bio-diagnostics. From the Clinical EditorExisting methods for the detection of small molecules are often not sensitive enough. Here, the authors developed aptamer functionalized SiO2@Au nanoshells for use in mass spectrometry, with very low detection limits. The new platform appeared to be simple and efficient and should be applicable in detection of clinical samples.

Highly sensitive impedimetric aptasensor based on covalent binding of gold nanoparticles on reduced graphene oxide with good dispersity and high density.

A series of gold nanoparticles (AuNPs) that were covalently bound to 2-aminothiophenol-functionalized reduced graphene oxide (Au-ATP-rGO) composites have been synthesized with well-dispersed and controllable surface coverage of AuNPs. Aptamer immobilization capacity studies demonstrated that the surface density of AuNPs played a key role in increasing the amount of anchoring aptamers to enhance the sensitivity of affinity based detection. With the composites possessing dense surface coverage of AuNPs as a versatile signal amplified platform, a label-free aptasensor for the sensitive and selective detection of small molecules (ochratoxin A in this case) has been developed using electrochemical impedance spectroscopy (EIS). A wide linear range of 0.1-200 ng mL(-1) was obtained with a low detection limit of 0.03 ng mL(-1) (S/N = 3). This work provides a universal strategy for the sensitive detection of a variety of targets in a truly label-free manner by means of changing the corresponding aptamer. The promising platform based on the combination of Au-ATP-rGO composites, EIS technique, and aptamers would have great potential applications in clinical diagnosis, environmental analysis, and food safety monitoring.

Mass Amplifying Probe for Sensitive Fluorescence Anisotropy Detection of Small Molecules in Complex Biological Samples

Fluorescence anisotropy (FA) is a reliable and excellent choice for fluorescence sensing. One of the key factors influencing the FA value for any molecule is the molar mass of the molecule being measured. As a result, the FA method with functional nucleic acid aptamers has been limited to macromolecules such as proteins and is generally not applicable for the analysis of small molecules because their molecular masses are relatively too small to produce observable FA value changes. We report here a molecular mass amplifying strategy to construct anisotropy aptamer probes for small molecules. The probe is designed in such a way that only when a target molecule binds to the probe does it activate its binding ability to an anisotropy amplifier (a high molecular mass molecule such as protein), thus significantly increasing the molecular mass and FA value of the probe/target complex. Specifically, a mass amplifying probe (MAP) consists of a targeting aptamer domain against a target molecule and molecular mass amplifying aptamer domain for the amplifier protein. The probe is initially rendered inactive by a small blocking strand partially complementary to both target aptamer and amplifier protein aptamer so that the mass amplifying aptamer domain would not bind to the amplifier protein unless the probe has been activated by the target. In this way, we prepared two probes that constitute a target (ATP and cocaine respectively) aptamer, a thrombin (as the mass amplifier) aptamer, and a fluorophore. Both probes worked well against their corresponding small molecule targets, and the detection limits for ATP and cocaine were 0.5 μM and 0.8 μM, respectively. More importantly, because FA is less affected by environmental interferences, ATP in cell media and cocaine in urine were directly detected without any tedious sample pretreatment. Our results established that our molecular mass amplifying strategy can be used to design aptamer probes for rapid, sensitive, and selective detection of small molecules by means of FA in complex biological samples.

Electrode array detector for microchip capillary electrophoresis

Selectivity and resolution for analyses conducted using microfluidic devices can be improved by increasing the total number of individual detection elements in the device. Here, a poly(dimethylsiloxane) capillary electrophoresis microchip was fabricated with an integrated electrode array for selective detection of small molecules. Eight individually addressable gold electrodes were incorporated in series after a palladium current decoupler in the separation channel of an electrophoresis microchip. The electrode array device was characterized using a mixture of biologically relevant analytes and xenobiotics: norepinephrine, 4-aminophenol, acetaminophen, uric acid, and 3,4-dihydroxyphenylacetic acid. Separation efficiencies as high as 9000 +/- 1000 plates (n = 3) for 3,4-dihydroxyphenylacetic acid and limits of detection as low as 2.6 +/- 1.2 microM (n = 3) for norepinephrine were obtained using this device. After characterizing the performance of the device, potential step detection was conducted at the array electrodes and selective detection achieved based upon differences in redox potentials for individual analytes. Utilization of potential step detection was particularly advantageous for resolving co-migrating species; resolution of 3,4-dihydroxy-l-phenylalanine from acetaminophen using potential control was demonstrated. Finally, a human urine sample was analyzed using potential step detection to demonstrate the applicability of this device for complex sample analysis.

Peptide-nanowire hybrid materials for selective sensing of small molecules.

The development of a miniaturized sensing platform for the selective detection of chemical odorants could stimulate exciting scientific and technological opportunities. Oligopeptides are robust substrates for the selective recognition of a variety of chemical and biological species. Likewise, semiconducting nanowires are extremely sensitive gas sensors. Here we explore the possibilities and chemistries of linking peptides to silicon nanowire sensors for the selective detection of small molecules. The silica surface of the nanowires is passivated with peptides using amide coupling chemistry. The peptide/nanowire sensors can be designed, through the peptide sequence, to exhibit orthogonal responses to acetic acid and ammonia vapors, and can detect traces of these gases from "chemically camouflaged" mixtures. Through both theory and experiment, we find that this sensing selectivity arises from both acid/base reactivity and from molecular structure. These results provide a model platform for what can be achieved in terms of selective and sensitive "electronic noses."

Parent Ion Scans of Large Molecules

The utility of parent ion scans for the selective detection of small molecules which yield indicative fragments in tandem mass spectrometry is well recognized. This work established the feasibility of parent (or precursor) ion experiments with large molecules such as proteins and oligonucleotides. Tandem mass spectrometry of proteins yields substantial and specific immonium ion fragmentation and fragments characteristic of post-translational modifications. Phosphoproteins are specifically detected by parent ion scans of the phospho group (PO3-) in the negative ion mode. The same ion allows mass measurements of oligonucleotides with improved signal-to-noise ratio. Scans for the parents of the oxonium ion of hexosamine distinguish glycoproteins from other proteins in mixtures. Parent ion scans of intact proteins is a novel concept which may find applications in the determination of post-translational modifications, in protein charting and in the study of the fragmentation behavior of large molecules. © 1997 by John Wiley & Sons, Ltd.

Detection of small molecules by magnetically tuned frequency-modulated atomic line sources

Small molecules such as NO, OH, I2, S2, SO2, NO2, and HCHO display discrete sharp electronic rotational-vibrational lines. Utilizing the Zeeman effect, one component of an atomic emission line can be made to exactly coincide with a sharp molecular line while the other component is shifted so that there is no overlap with this line. When large molecules undergo electronic transitions it is not possible to resolve the rotational structure in the vast majority of cases. Therefore, the difference in absorption between the σ± components is proportional to the density of the molecules showing sharp absorption but is not influenced by other molecules. These phenomena can be used to achieve highly sensitive and selective detection of small molecules.