Eu3+ doped ethylenediamine functionalized UiO-66 probe for fluorescence sensing of formaldehyde.

The development of probes with selectivity and prompt detection of aldehydes molecules is of great importance for protecting human health and public security. Herein, a system based on ethylenediamine (EDA) functionalized and Eu3+-doped UiO-66, namely EDA-Eu3+@UiO-66, was designed to detect formaldehyde molecules. Based on the "antenna effect" of lanthanide elements, UiO-66 transfers the absorbed energy to Eu3+ ions and emits characteristic fluorescence belonging to Eu3+. By using the fluorescence peaks of UiO-66 and Eu3+ respectively, a ratiometric fluorescence sensing probe can be constructed. Formaldehyde molecules react with the -NH2 on the surface of EDA-Eu3+@UiO-66 through an aldehyde-amine condensation reaction and connect to the functionalized surface of UiO-66. Due to the absorption of excitation light energy by formaldehyde molecules, the energy transfer efficiency from UiO-66 to Eu3+ ions is reduced, resulting in the fluorescence quenching of EDA-Eu3+@UiO-66, thus achieving selective detection of formaldehyde. The fabricated sensing platform successfully detected residual formaldehyde in frozen shrimp tail samples. The system was also used to respond to formaldehyde vapor, and a significant fluorescence quenching effect was observed. This strategy provides a sensitive, selective, and reliable method for the visual sensing of formaldehyde.

MicroRNA-21 electrochemiluminescence biosensor based on Co-MOF-N-(4-aminobutyl)-N-ethylisoluminol/Ti3C2Tx composite and duplex-specific nuclease-assisted signal amplification.

A novel electrochemiluminescence (ECL) biosensor for the determination of microRNA-21 (miRNA-21) was developed, based on a hybrid luminescent Co-MOF-ABEI/Ti3C2Tx composite as an ECL luminophore combined with a duplex-specific nuclease (DSN)-assisted signal amplification strategy. The synthesized Co-MOF-ABEI/Ti3C2Tx composite carrying N-(4-aminobutyl)-N-ethylisoluminol (ABEI) exhibited strong and stable ECL in the presence of reactive oxygen species (ROS). The ECL biosensor was fabricated by adsorbing Co-MOF-ABEI/Ti3C2Tx onto a glassy carbon electrode and covalently coupling the probe DNA onto the surface of the Co-MOF-ABEI/Ti3C2Tx-modified electrode. In the presence of the target miRNA-21, the DSN selectively cleaved the complementary DNA section (S1) to miRNA-21, resulting in the release of the transduction section (S2) and the reuse of miRNA-21 in the subsequent amplification cycle. The interaction of the stem-loop structure of the probe DNA with the Co-MOF-ABEI/Ti3C2Tx-modified glassy carbon electrode with S2 strands led to the opening of the annular part of the probe DNA. Then, the opened guanine (G)-rich sequences of probe DNA were exposed and folded into a hemin/G-quadruplex DNAzyme in the presence of hemin. The catalysis of H2O2 to ROS by the hemin/G-quadruplex DNAzyme significantly enhanced ECL intensity, and this intensity was logarithmically proportional to the concentration of target miRNA-21 between 0.00001 and 10 nM, having a limit of detection of 3.7 fM. The designed ECL biosensor can  detect miRNA-21 extracted from HeLa cells, indicating its promising application in clinical diagnosis and disease prognosis analysis.

Electrochemiluminescent emission potential tunable Cu-Zn-In-S/ZnS nanocrystals for multiplex microRNAs potential-resolved detection.

The development of a multi-target simultaneous detection electrochemiluminescence (ECL) strategy remains a great research interest, however, the limited choice of ECL luminophores is the main limitation holding the field back. In this study, a band gap tunable Cu-Zn-In-S/ZnS nanocrystals (CZIS/ZnS NCs) was synthesized and applied to a potential-resolved ECL detection strategy. By changing the Cu ratio in the precursor, the CZIS/ZnS NCs ECL emission spectrum and emission potential were tuned from 480 to 750 nm and -2.10 to -1.11 V, respectively. In addition, an ECL biosensor was fabricated with CZIS/ZnS NCs as signal reporters to detect three types of microRNAs, which could sensitively and selectively determine microRNA-21, microRNA-141, and microRNA-155 in a single cathodic ECL process. The results showed that the ECL intensity was directly linear to the logarithm of the concentration of microRNA-21, microRNA-141, and microRNA-155 from 0.00001 to 10 nM with detection limits of 2.2, 2.6, and 2.7 fM, respectively. This study demonstrates that the emission potential tunable CZIS/ZnS NCs can be employed as a promising alternative to the toxic II-V and II-V NCs to simultaneously detect multiple disease markers, and can guide the further rational design of both ECL luminophores and multi-analyte ECL sensors.

Universal Strategy for Improving the Sensitivity of Detecting Volatile Organic Compounds by Patterned Arrays.

The diffusion of target analytes is a determining factor for the sensitivity of a given gas sensor. Surface adsorption results in a low-concentration region near the sensor surface, producing a concentration gradient perpendicular to the surface, and drives a net flux of molecules toward solid reactive reagents on the sensor surface, that is, vertical diffusion. Here, organic semiconductor supramolecules were patterned into micromeshed arrays to integrate vertical and horizontal diffusion pathways. When used as a gas sensor, these arrays have an order of magnitude higher sensitivity than traditional film-based sensors. The sensor sensitivity ramp down with the increase in coverage density of reactive reagents, yielding two linear regions demarcated by 0.3 coverage, which are identified by the experimental results and simulations. The universal nature of template-assisted patterning allows adjustments in the composition, size, and shape of the constituent material, including nanofibers, nanoparticles, and molecules, and thus serves to improve the sensitivity of gas sensors for detecting various volatile organic compounds.

Nanomaterial-based gas sensors used for breath diagnosis.

Gas-sensing applications commonly use nanomaterials (NMs) because of their unique physicochemical properties, including a high surface-to-volume ratio, enormous number of active sites, controllable morphology, and potential for miniaturisation. NM-based gas sensors, as a noninvasive, real-time technique, are a promising candidate for monitoring human breath. This review focuses on NM-based gas sensors used for breath diagnosis. First we describe some representative biomarkers of diseases that are detectable in breath and requirements for breath sensors. Then we review electrical, optical and mass-sensitive gas sensors in terms of these performance requirements, together with describing the detection capability of these sensors for trace concentrations of biomarkers and their initial attempts to diagnose disease. Moreover, we discuss breath sensor platforms with a multivariable sensing system, wireless communication and breath sampling, essential for predictive, preventive, personalised, and participatory ("P4") medicine. Finally, we conclude with problems and challenges associated with the selectivity, humidity and validation of breath sensors. We hope that this article will inspire the development of high-performance gas sensors based on novel NMs.

Electrogenerated chemiluminescence biosensing method based on 5-hydroxymethylcytosine antibody and PDDA-CNTs nanocomposites for the determination of 5-hydroxymethylcytosine double-stranded DNA.

A highly sensitive electrogenerated chemiluminescence (ECL) method was developed for trace analysis of 5-hydroxymethylcytosine double-stranded DNA (5-hmC-dsDNA). The poly-(dimethyldiallyl ammonium chloride)/multiwalled carbon nanotubes composite was assembled on a bare glassy carbon electrode (GCE) to provide high specific surface area on which the loadable capacity of 5-hmC-dsDNA and 5-hmC antibody can be greatly increased. The derivative of ruthenium (II) bibyridine, Ru (bpy)2 (dcbpy)NHS, coupled with 5-hmC antibody to activate an ECL reaction when the applied potential was biased at 1.4 V vs. Ag/AgCl. The loading ratio of substrates were optimized to enhance the detection sensitivity of 5-hmC-dsDNA. It was found that the ECL intensity was a piecewise linear function of the concentration of 5-hmC-dsDNA over the range of 1.0 × 10-11-2.0 × 10-9 M. A linear relationship of I = 6850.3 C(nM) + 863.8 (R = 0.9954) was obtained from 0.01 to 0.2 nM, while the fitting equation of I = 3840.0 C(nM) + 1392.4 (R = 0.9974) is for the concentration range of 0.2 - 2.0 nM. The detectable low limit can reach to 2.3 × 10-12 M. Formation of the antigen-antibody immunocomplex in highly concentrated solutions should undertake most of the responsibility for a decrease in slope. Furthermore, reliability, reproducibility and practicability of the ECL method have been proved to perform well, even in real bio-tissues, suggesting promising prospect in early diagnosis of cancer.

Signal-on electrogenerated chemiluminescence biosensor for ultrasensitive detection of microRNA-21 based on isothermal strand-displacement polymerase reaction and bridge DNA-gold nanoparticles.

MicroRNA-21 (miRNA-21) is a promising diagnostic biomarker for breast cancer screening and disease progression. A sensitive and selective strategy for the quantitative determination of miRNA-21 is of great significance in the early diagnosis of cancers. Herein, a novel electrogenerated chemiluminescence (ECL) biosensor was designed for the detection of miRNA-21 with dual signal amplification based on isothermal strand-displacement polymerase reaction (ISDPR) and bridge DNA-gold nanoparticles (AuNPs) nanocomposites. The ECL biosensor was fabricated by self-assembling a thiolated capture probe (SH-CP) on the surface of a gold electrode. The target miRNA-21 initiated the phi29 DNA polymerase-mediated ISDPR, which could generate large numbers of single-stranded DNA (assistant DNA) with accurate and comprehensive nucleotide sequences. The assistant DNA was captured by the SH-CP self-assembled on the Au electrode and further hybridized with bridge DNA-AuNPs nanocomposites, more biotins can be captured on the electrode surface. Afterward, a streptavidin-modified Ru (bpy)32+ complex (SA-Ru) was bound to the bridge DNA-AuNPs nanocomposites via a specific interaction between biotin and streptavidin to produce a strong ECL signal. The ECL intensity was logarithmically proportion to the concentration of target miRNA-21 over a range from 0.01 fM to 10,000 fM with a detection limit of 3.2 aM. The proposed ECL biosensor was successfully applied to detect miRNA-21 in total RNA samples extracted from human breast cancer cells, and it showed great potential for early cancer diagnosis based on miRNA as a biomarker.

Signal-Off Electrogenerated Chemiluminescence Biosensing Platform Based on the Quenching Effect between Ferrocene and Ru(bpy)32+-Functionalized Metal-Organic Frameworks for the Detection of Methylated RNA.

N6-methyladenine (m6A), one of the most common chemical modifications of eukaryotic RNA, participates in many important biological processes. An effective strategy for the quantitative determination of m6A is of great significance. Herein, we used methylated microRNA-21 (miRNA21) as the model target to propose a simple and sensitive electrogenerated chemiluminescence (ECL) biosensing platform to detect a specific m6A RNA sequence. This strategy is based on the fact that the anti-m6A-antibody can specifically recognize and bind to the m6A site in the RNA sequence, resulting in a quenching effect between Ru(bpy)32+-functionalized metal-organic frameworks and ferrocene. Luminescent metal-organic frameworks (Ru@MOFs) not only act as ECL indicators but also serve as nanoreactors for the relative ECL reactions owing to their porous or multichannel structure, which overcomes the fact that Ru(bpy)32+ is easily released when used for aqueous-phase detection, thus enhancing the ECL efficiency. Moreover, the ECL method has fewer modification steps and uses only one antibody to recognize the target RNA sequence, which simplifies the operation process and reduces the detection time, presenting a wide linear range (0.001-10 nM) for m6A RNA determination with a low detection limit (0.0003 nM). Additionally, this developed strategy was validated for m6A RNA detection in human serum. Thus, the ECL biosensing method provides a new method for m6A RNA determination that is simple, highly specific, and sensitive.

Label-free and amplified electrogenerated chemiluminescence biosensing for the detection of thymine DNA glycosylase activity using DNA-functionalized gold nanoparticles triggered hybridization chain reaction.

Effective detection of thymine DNA glycosylase (TDG) activity is extremely crucial and urgent for epigenetic research. Herein, a novel label-free electrogenerated chemiluminescence (ECL) biosensing method was developed for the detection of TDG activity using DNA-functionalized gold nanoparticles (DNA-AuNPs) triggered hybridization chain reaction (HCR). In this assay, the thiol modified hairpin probe DNA (hp-DNA) with 5' overhangs and one mismatched base pair of guanines: thymine (G: T) in the stem part was boned onto gold electrode. TDG specifically removed T base of the G: T mismatch to produce apyrimidinic (AP) sites through the N-glycosidic bond hydrolysis. The AP site was then cleaved by the catalysis of Endonuclease IV (EnIV) to generate dsDNA containing a free 3' end in the long sequence, which serves as a complementary sequence to hybridize with the specific sequence (ssDNA1) of DNA-AuNPs. Then, the functionalized DNA-AuNPs with initiator strands (ssDNA2) could trigger HCR to form nicked double helices DNA polymer which can embed numerous ECL indicator, Ru(phen)32+, resulting in significantly increased ECL signal. The proposed strategy combined the amplification function of DNA-AuNPs triggered HCR and the inherent high sensitivity of the ECL technique, a detection limit of 1.1 × 10-5 U/µL (0.0028 ng/mL) for TDG determination was obtained. In addition, this method was successfully applied to evaluate TDG activity in cancer cell, which provides great possibility for TDG activity assay in related clinical diagnostics.

Sensitive electrogenerated chemiluminescence biosensing method for the determination of DNA hydroxymethylation based on Ru(bpy)32+-doped silica nanoparticles labeling and MoS2-poly(acrylic acid) nanosheets modified electrode.

5-Hydroxymethylcytosine (5-hmC), an oxidation product of 5-mC (5-methylcytosine), is presented in DNA of most mammalian cells and play an important role in the alteration of cancer-related genes. Herein, a sensitive electrogenerated chemiluminescence (ECL) biosensing method for the determination of 5-hmC in DNA (5-hmC DNA) was established on the basis of chemical modification and nanomaterial amplification. First, electrochemically reduced molybdenum disulfide-poly(acrylic acid) (rMoS2-PAA) nanosheets were used to modify glassy carbon electrode (GCE) to form an ECL biosensing electrode (rMoS2-PAA/GCE) which has large accessible surface area to immobilize more DNA. Then, a capture probe with amino group was hybridized with the target 5-hmC DNA and immobilized on the surface of rMoS2-PAA/GCE via amido bond. When cysteamine was introduced, the M.HhaI methyltransferase (M.HhaI) was used as specific recognition element to replace the hydroxyl group of 5-hmC by thiol and generated the amine-derivated DNA. Finally, surface chemically activated Ru(bpy)32+-doped silica (Ru@SiO2) nanoparticles, carriers of ECL reagents, were employed as signal amplification unit which covalently bonded to the amine-derivated DNA resulting in an increased ECL intensity. The increased ECL intensity was linearity to the 5-hmC DNA concentration in a range from 5.0 × 10-14 M to 1.0 × 10-11 M, with a lower detection limit of 1.2 × 10-14 M. Besides, the proposed method also displayed a good selectivity to 5-hmC in the presence of 5-C and 5-mC. Moreover, the developed biosensing method was successfully employed to monitor human urine sample.

An ultrasensitive electrochemical DNA biosensor based on graphene/Au nanorod/polythionine for human papillomavirus DNA detection.

An ultrasensitive electrochemical DNA biosensor for human papillomavirus (HPV) detection was developed by electrochemical impedance spectroscopy and differential pulse voltammetry. A capture probe was immobilized on a glassy carbon electrode modified with graphene/Au nanorod/polythionine (G/Au NR/PT). Two auxiliary probes were designed and used to long-range self-assemble DNA nanostructure. The target DNA can connect DNA structure to the capture probe on the electrode surface. [Ru(phen)3](2+) was selected as a redox indicator for amplifying electrochemical signal significantly. Enhanced sensitivity was obtained through combining the excellent electric conductivity of G/Au NR/PT architecture and the long-range self-assembly DNA nanostructure with the multi-signal amplification. The DNA biosensor displayed excellent performance for HPV DNA detection over the range from 1.0×10(-13) to 1.0×10(-10) mol/L with a detection limit of 4.03×10(-14) mol/L. Furthermore, the proposed method can also be used for the detection of HPV DNA in human serum samples and provides a potential application of DNA detection in clinic research.