Isoelectric Bovine Serum Albumin: Robust Blocking Agent for Enhanced Performance in Optical-Fiber Based DNA Sensing

Phase separation of triton X-100 and bovine serum albumin mixture: Impacts of nature and composition of polyols on associated physicochemical parameters

Bovine serum albumin (BSA) is widely used in tissue engineering and pharmaceutical research. It is readily available as a byproduct of the cattle industry, and collected from blood. In this study, we conducted a physicochemical investigation of the phase separation in a mixture of Triton X-100 (TX-100) and BSA, influenced by various polyols, using the well-established cloud point (CP) determination method. The addition of polyols resulted in a significant reduction in CP values for the TX-100 + BSA mixture. The magnitudes of CP in the experimental system were highly varied with different polyols and followed the order of: [Formula: see text] Under identical conditions, the system exhibited maximum solubility in the xylose solution and minimum solubility in the maltose solution. The positive ΔGc0 values were acquired in all working medium imply the nonspontaneity of phase transition in the TX-100 + BSA system. At lower polyol contents, the negative values of standard enthalpy (∆Hc0) and standard entropy (∆Sc0) changes were observed, suggesting that electrostatic forces dominated as the driving force for clouding. At highest employed polyols concentration in some case, the positive values for ∆Hc0 and ∆Sc0 were achieved, which indicated that hydrophobic interactions likely dominate the phase partitioning of the amphiphile and protein mixture. Additionally, entropy-enthalpy compensation parameters were calculated and analyzed with a rational approach. Molecular docking analysis further demonstrated the presence of hydrogen bonds and hydrophobic interactions between TX-100 and BSA.

The influence of charge on the translation of the sandwich ELISA approach to electronic biosensors

The sandwich approach, whereby an antigen is captured by a primary antibody and detected by a secondary antibody, is commonly used to improve the selectivity and sensitivity of enzyme-linked immunosorbent assays (ELISA). This work details the experimental factors that impact the reliable translation of this sandwich approach to two commonly used electronic biosensors, namely potentiometric and impedimetric biosensors. Previous studies have demonstrated the Debye screening limitations associated with potentiometric biosensors. However, the correlation between the ionic strength of the measurement buffer and the impedimetric biosensing response has not been studied. Potentiometric biosensors were able to successfully detect the primary antibody and the target antigen by decreasing the ionic strength of the phosphate buffered saline (PBS) measurement buffer from 1x PBS to 0.01x PBS. However, the secondary antibody used for the selective signal amplification was not reliably detected. Therefore, the sandwich approach is not viable for potentiometric sensing at biologically relevant ionic strengths, due to the Debye screening effect. Alternatively, decreasing the ionic strength of the measurement buffer allowed for the successful translation of the sandwich approach to impedimetric biosensors. Impedimetric biosensing literature typically attributes a measured increase in the charge transfer resistance to an increase in the thickness of the immobilized biolayer. However, this work highlights the influence that both the charge and thickness of the biolayer have on the transport of the redox couple. Decreasing the ionic strength of the measurement buffer lowers the molecular charge screening effect. This permits the transport of a positively charged redox probe through a negatively charged immobilized biolayer via migration and diffusion. The results demonstrate that the use of a buffer at a lower, yet biologically relevant ionic strength allows for the successful translation of the sandwich approach to impedimetric biosensors.

The non-negligible non-specific adsorption of oligonucleotides in target-immobilized Mag-SELEX

Target-immobilized magnetic beads-based Systematic Evolution of Ligands by Exponential Enrichment (target-immobilized Mag-SELEX) has emerged as a powerful tool for aptamer selection owing to its convenience, efficiency, and versatility. However, in this study we systematically investigated non-specific adsorption in target-immobilized Mag-SELEX and found that the non-specific adsorption of the oligonucleotides to target-labeled magnetic beads was comparable to that of the screening libraries, indicating a substantial portion of captured sequences likely stem from non-specific adsorption. Longer nucleic acid sequences (80 nt and above, such as polyA80 and yeast tRNA) were found to attenuate this non-specific adsorption, with more complex higher-order structures demonstrating greater efficacy, while dNTP and short sequences such as primer sequences (20 nt), polyT(59), or polyA(59), did not possess this capability. Various evidence suggested that hydrophobic interactions and other weak interactions may be the primary underlying cause of non-specific adsorption. Additionally, surface modification of magnetic beads with polar molecule polyethylene glycol (PEG) also yielded a significant reduction in non-specific adsorption. In conclusion, our research underscores the critical importance of closely monitoring non-specific adsorption in target-immobilized Mag-SELEX.

Phase separation, aggregation, and complexation of triton-X100 and bovine serum albumin mixture: A combined cloud point and UV-visible spectroscopic approaches

Phase separation and aggregation behaviour of triton X-100 (TX-100) and bovine serum albumin (BSA) mixture were investigated using cloud point and UV-visible spectroscopic techniques. The effects of various hydrotropes (HYTs) - namely, sodium salicylate (SS), sodium benzoate (SB), glycerol (Glyc), and 4-aminobenzoic acid (4-ABA) - on the cloud point (CP) of TX-100 + BSA were determined. The obtained CP values for the mixed system in the presence of HYTs followed the order: The measured critical micellization concentration (CMC) values of the TX-100 + BSA mixture were found to be significantly altered with varying amounts of BSA. The calculated free energy of clouding and micellization indicated the non-spontaneous nature of the phase transition and the spontaneous association of the TX-100 + BSA mixture. The non-spontaneity of phase separation decreased with increasing concentrations of HYTs. The enumerated values of ∆Hco and ∆Sco were consistently recorded as negative and positive magnitudes, respectively, in all aqueous HYTs media. The clouding process occurred due to a combination of hydrophobic and electrostatic interactions. The binding constant of the mixed system was determined employing the UV-vis spectroscopic method using the Benesi-Hildebrand equation.

Bovine serum albumin-liposome stabilized high oil-phase emulsion: Effect of liposome ratio on interface properties and stability

This study aimed to solve the issue of poor lipophilicity of natural bovine serum albumin (BSA) by combining with liposomes (Lips) to stabilize high oil-phase emulsions (HOPEs). The interaction between BSA and Lips was mainly driven by hydrophobic forces, followed by hydrogen bonding. The secondary structure and tertiary structure of BSA were characterized and indicated that the addition of Lips promoted the structural expansion of BSA exposing the hydrophobic groups inside. Interfacial adsorption behaviours were assessed through dynamic interfacial tension, three-phase contact angle, and quartz crystal microbalance with dissipation. These results indicated that BSA-Lips crosslinking improved wettability, promoting adsorption and rearrangement at the oil-water interface, thereby resulting in a dense interfacial layer. The emulsifying efficacy of BSA-stabilized HOPEs also displayed a distinct Lips dependency. Varying the BSA-to-Lips ratio transformed their consistency from flowing to semi-solid, reinforcing the gel network. Under optimal conditions (BSA: Lips = 1:1), the droplet size of BSA-Lips stabilized HOPEs reached a minimum with a highly uniform distribution. Moreover, a 1:1 BSA to Lips ensured outstanding storage, thermal, and centrifugal stability for the HOPEs. This work provides valuable references for the interaction between protein and Lips, guiding the development of highly stable HOPEs stabilizers.

Polymersomes for Therapeutic Protein and Peptide Delivery: Towards Better Loading Properties

Therapeutics based on proteins and peptides have profoundly transformed the landscape of treatment for diseases, from diabetes mellitus to cancers, yet the short half-life and low bioavailability of therapeutic proteins and peptides hinder their wide applications. To break through this bottleneck, biomolecules-loaded polymersomes with strong adjustability and versatility have attracted more and more attentions recently. Loading proteins or peptides into polymersomes is the first but extremely important step towards developing high-quality formulation products. However, increasing protein and peptide loading content is quite challenging due to the inherent nature of self-assembled vesicle formation mechanism and physiochemical characteristics of biomacromolecules. This review highlights the potential of polymersomes as the next-generation therapeutic proteins and peptides carrier and emphatically introduces novel approaches and recent progress to achieve satisfactory encapsulation capability of polymersomes for proteins and peptides. On the one hand, with the help of intermolecular interactions, such as electrostatic, lipid-protein, and hydrophobic interactions, the drug loading could be significantly improved. On the other hand, loading improvement could be attained through innovation of preparation methods, ranging from modified traditional film hydration techniques to the novel phase-guided assembly method.

An ultrasensitive J-shaped optical fiber LSPR aptasensor for the detection of Helicobacter pylori

The development of label-free and sensitive detection of pathogenic bacteria is of great significance for disease prevention and public health protection. In this study, an originally bent structure, named as J-shaped optical fiber probe, was first designed to engineer a localized surface plasmon resonance (LSPR) aptamer biosensor for the rapid and ultrasensitive detection of Helicobacter pylori (H. pylori). The J-shaped optical fiber probe exhibited a significant improvement in refractive index sensitivity (RIS) and LSPR signal response. Meantime, the original sequence of aptamer was truncated in order to effectively capture H. pylori on the optical fiber surface. Besides, a spacer nucleic acid with short stem-loop structure was adopted to control the aptamer density on gold nanoparticles (AuNPs) on the surface of the J-shaped optical fiber probe, which displayed a further enhancement in LSPR signal response. Benefitting from these creative designs, the proposed LSPR biosensor can realize label-free and sensitive detection of H. pylori with a detection limit as low as 45 CFU/mL and a wide linear range from 1.0 × 102 CFU/mL to 1.0 × 108 CFU/mL. At the same time, the sensing strategy can detect the pathogenic bacteria from actual water samples in one step just in 30 min without any sample pretreatment. Due to the advantages of ease-to-preparation, high sensitivity, and rapid analysis, this proposed J-shaped optical fiber LSPR aptasensor can provide a potential strategy for point-of-caring detection of pathogenic bacteria in environmental monitoring and disease diagnosis.

Fiber-Optic-Based Biosensor as an Innovative Technology for Point-of-Care Testing Detection of Foodborne Pathogenic Bacteria To Defend Food and Agricultural Product Safety

Food safety is a concerning issue globally. Foodborne-pathogenic-bacteria-derived foodborne disease outbreaks have increased the threat to human health. The accurate and rapid detection of foodborne bacteria is of great significance for food safety. A fiber-optic-based biosensor has emerged as a powerful technique for the point-of-care testing of foodborne bacteria in food and agricultural products. This Perspective discusses the opportunities and challenges of fiber-optic-based biosensors for foodborne bacteria detection. The corresponding solution strategies to promote the application of this innovative technology in food and agricultural product detection for food safety and human health are also discussed and proposed.

Recent Progress in Functional-Nucleic-Acid-Based Fluorescent Fiber-Optic Evanescent Wave Biosensors

Biosensors capable of onsite and continuous detection of environmental and food pollutants and biomarkers are highly desired, but only a few sensing platforms meet the "2-SAR" requirements (sensitivity, specificity, affordability, automation, rapidity, and reusability). A fiber optic evanescent wave (FOEW) sensor is an attractive type of portable device that has the advantages of high sensitivity, low cost, good reusability, and long-term stability. By utilizing functional nucleic acids (FNAs) such as aptamers, DNAzymes, and rational designed nucleic acid probes as specific recognition ligands, the FOEW sensor has been demonstrated to be a general sensing platform for the onsite and continuous detection of various targets ranging from small molecules and heavy metal ions to proteins, nucleic acids, and pathogens. In this review, we cover the progress of the fluorescent FNA-based FOEW biosensor since its first report in 1995. We focus on the chemical modification of the optical fiber and the sensing mechanisms for the five above-mentioned types of targets. The challenges and prospects on the isolation of high-quality aptamers, reagent-free detection, long-term stability under application conditions, and high throughput are also included in this review to highlight the future trends for the development of FOEW biosensors capable of onsite and continuous detection.

Haem-Mediated Albumin Biosensing: Towards Voltammetric Detection of PFOA

The haem group is a promising redox probe for the design of albumin-based voltammetric sensors. Among the endogenous ligands carried by human serum albumin (hSA), haem is characterised by a reversible redox behaviour and its binding kinetics strongly depend on hSA's conformation, which, in turn, depends on the presence of other ligands. In this work, the potential applicability of haem, especially hemin, as a redox probe was first tested in a proof-of-concept study using perfluorooctanoic acid (PFOA) as model analyte. PFOA is known to bind hSA by occupying Sudlow's I site (FA7) which is spatially related to the haem-binding site (FA1). The latter undergoes a conformational change, which is expected to affect hemin's binding kinetics. To verify this hypothesis, hemin:albumin complexes in the presence/absence of PFOA were first screened by UV-Vis spectroscopy. Once the complex formation was verified, haem was further characterised via electrochemical methods to estimate its electron transfer kinetics. The hemin:albumin:PFOA system was studied in solution, with the aim of describing the multiple equilibria at stake and designing an electrochemical assay for PFOA monitoring. This latter could be integrated with protein-based bioremediation approaches for the treatment of per- and polyfluoroalkyl substances polluted waters. Overall, our preliminary results show how hemin can be applied as a redox probe in albumin-based voltammetric sensing strategies.

Group-targeting sulfonamides via an evanescent-wave biosensor based on rational designed coating antigen

In order to effectively monitor a wide variety of sulfonamides residues in the environment, group-targeting immunoassay based on the group-specific antibodies has attracted great attentions, which can realize the detection of a group of contaminants in environment as many as possible even the unrecognized ones. Indirect competitive immunoassay is generally adopted for small molecule detection however the rational design of immobilized coating antigen for improved recognition capability on the solid surface is far from enough. To cover the research gap, we proposed the design criteria of coating antigen for surface-based indirect competitive immunoassay based on the molecular docking. Taking the group-specific antibodies against sulfonamides (SA) as a proof-of-concept, a hapten with a linking arm with 3 methyl groups was selected to synthesize the coating antigen. Through surface immobilization of coating antigen, a portable biosensor for group-targeting immunoassay of sulfonamides was developed and demonstrated excellent performance with detection limits lower than 0.6 μg/L for four SA variants, and the cross-reactivities of 148-215 % relative to sulfadiazine. The recovery rates of SAs in liquid milk ranges from 87 to 97 %, which confirmed the application potential of this method in the determination of SAs. Its capability to measure total SAs in a simple and low-cost way would pave the way for a variety of application fields.

Flexible Label-Free Platinum and Bio-PET-Based Immunosensor for the Detection of SARS-CoV-2

The demand for new devices that enable the detection of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) at a relatively low cost and that are fast and feasible to be used as point-of-care is required overtime on a large scale. In this sense, the use of sustainable materials, for example, the bio-based poly (ethylene terephthalate) (Bio-PET) can be an alternative to current standard diagnostics. In this work, we present a flexible disposable printed electrode based on a platinum thin film on Bio-PET as a substrate for the development of a sensor and immunosensor for the monitoring of COVID-19 biomarkers, by the detection of L-cysteine and the SARS-CoV-2 spike protein, respectively. The electrode was applied in conjunction with 3D printing technology to generate a portable and easy-to-analyze device with a low sample volume. For the L-cysteine determination, chronoamperometry was used, which achieved two linear dynamic ranges (LDR) of 3.98-39.0 μmol L-1 and 39.0-145 μmol L-1, and a limit of detection (LOD) of 0.70 μmol L-1. The detection of the SARS-CoV-2 spike protein was achieved by both square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) by a label-free immunosensor, using potassium ferro-ferricyanide solution as the electrochemical probe. An LDR of 0.70-7.0 and 1.0-30 pmol L-1, with an LOD of 0.70 and 1.0 pmol L-1 were obtained by SWV and EIS, respectively. As a proof of concept, the immunosensor was successfully applied for the detection of the SARS-CoV-2 spike protein in enriched synthetic saliva samples, which demonstrates the potential of using the proposed sensor as an alternative platform for the diagnosis of COVID-19 in the future.

Oligonucleotide-Blocked Streptavidin for Biotinylation Analysis

Binding between streptavidin, or its homologues, to biotin is one of the most widely exploited biological interactions in the biomedical sciences. Controlling the extent of biotinylation is important for meeting the requirements of the intended design and to preserve the native function of the biotin recipient. Within the protein world, a"trial-and-error" optimization approach toward biotinylation reaction conditions is often necessary due to widely varying properties of proteins. Therefore, product analysis is important. We show here that a oligonucleotide-blocked streptavidin, effectively "monovalent streptavidin", can tag biotin moieties individually and the tagged products visualized via a polyacrylamide gel shift assay to reveal the product distribution, i.e., [protein-(biotin)_n] products where n = 1, 2, 3, etc. This is in contrast, and complementary, to current commercially available analytical reagents for biotinylation characterization, which use an absorbance or fluorescence signal to yield the mean number of biotin moieties.

Screening of Endocrine Disrupting Potential of Surface Waters via an Affinity-Based Biosensor in a Rural Community in the Yellow River Basin, China

Overcoming the limitations of traditional analytical methods and developing technologies to continuously monitor environments and produce a comprehensive picture of potential endocrine-disrupting chemicals (EDCs) has been an ongoing challenge. Herein, we developed a portable nuclear receptor (NR)-based biosensor within 90 min to perform highly sensitive analyses of a broad range of EDCs in environmental water samples. Based on the specific binding of the fluorescence-labeled NRs with their ligands, the receptors were attached to the EDC-functionalized fiber surface by competing with EDCs in the samples. The biosensor emitted fluorescence due to the evanescent wave excitation, thereby resulting in a turn-off sensing mode. The biosensor showed a detection limit of 5 ng/L E₂-binding activity equivalent (E₂-BAE) and 93 ng/L T₃-BAE. As a case study, the biosensor was used to map the estrogenic binding activities of surface waters obtained from a rural community in the Yellow River basin in China. When the results obtained were compared with those from the traditional yeast two-hybrid bioassay, a high correlation was observed. It is anticipated that the good universality and versatility exhibited by this biosensor for various EDCs, which is achieved by using different NRs, will significantly promote the continuous assessment of global EDCs.

Poly(amidoamine) dendrimer immunosensor for ultrasensitive gravimetric and electrochemical detection of matrix metalloproteinase-9

Monitoring the level of matrix metalloproteinase-9 (MMP-9) and inhibiting its expression is important for the diagnosis and treatment of various diseases. However, the analysis of MMP-9 is challenging owing to its very low content in the blood, especially at the early stages of diseases. Therefore, we developed an ultrasensitive and easy-to-use immunosensor based on a three-dimensional (3D) bioplatform for the determination of the total MMP-9 concentration in plasma. The used 3D bioplatform (G2 poly(amidoamine) dendrimer; PAMAM) improved the sensitivity of the determination by significantly expanding the surface area of the receptor layer. The antigen-antibody recognition process was controlled by quartz crystal microbalance with dissipation (QCM-D) and electrochemical impedance spectroscopy (EIS). The effect of the orientation of antibody molecules in the sensing layer on the work parameters of the immunosensor was analyzed using unmodified PAMAM (PAMAM-NH₂) and PAMAM functionalized with -COOH groups (PAMAM-COOH). The developed immunosensor based on PAMAM-NH₂ was characterized by a lower detection limit (LOD = 2.0 pg⋅mL^-1) and wider analytical range (1·10^-4 - 5 μg⋅mL^-1 for EIS and QCM-D) compared to PAMAM-COOH immunosensor (EIS: 1·10^-4 - 0.5 μg⋅mL^-1; QCM-D: 5·10^-4 - 0.5 μg⋅mL^-1). The functionality of the proposed device was verified in spiked plasma. The recoveries determined in commercial human and rat plasma and noncommercial rat plasma were very close to the value of 100% and in the range of 96-120% for Au/PAMAM-NH₂/Ab and Au/PAMAM-COOH/Ab immunosensors, respectively. The designed analytical devices showed high selectivity and sensitivity without the use of any amplifiers such as metal nanoparticles or enzymes.

Fiber-integrated WGM optofluidic chip enhanced by microwave photonic analyzer for cardiac biomarker detection with ultra-high resolution

Cardiac troponin I (cTnI) plays an important role in emergency diagnosis of cardiovascular diseases, which exists predominately in the form of cardiac troponin I-C (cTnI-C) complex. We proposed a fiber-integrated optofluidic chip immunosensor with time-delay-dispersion based microwave photonic analyzer (MPA) for cTnI-C detection. The whispering gallery mode (WGM) fiber probe was fabricated by embedding a polydopamine functionalized hollow glass microsphere (HGMS) into the etched capillary-fiber structure, and the WGMs could be excited through the efficient coupling between the thin-wall capillary and the HGMS. The reflective WGM optofluidic chip functioned as a wavelength tuner to construct fiber ring laser cavity, whose laser output wavelength was cTnI-C concentration-dependent. The tiny wavelength variation of sensing laser was converted into a radio-frequency (RF) response, which was retrieved by measuring the change of RF-domain free spectrum range (FSR) in time-delay-dispersion based MPA, and the quantitative detection of cTnI-C complex can be achieved with high resolution. Experimental results show that this immunosensor had a limit of detection (LOD) of 0.59 ng/mL, and a detection resolution of 1.2 fg/mL. The relative resolving power was 10²-10⁴-fold higher than that of others optical fiber cTnI biosensors. The proposed fiber-integrated optofluidic chip provides an innovative lab-on-chip diagnostic tool for myocardial damage.

A sandwich-based evanescent wave fluorescent biosensor for simple, real-time exosome detection†

Exosomes are regarded as a promising biomarker for the noninvasive diagnosis and treatment of diseases. The value of exosomes for medical research has promoted the search for a fast, efficient, and sensitive detection method. This study reported a sandwich-based evanescent wave fluorescent biosensor (S-EWFB) for exosome detection. A two-step strategy was implemented to take advantages of the simple binding of fluorescent probes with exosomes via the hydrophobic interaction between the cholesteryl and phospholipid bilayer membrane, as well as real-time detection on an evanescent wave liquid-solid interface based on CD63 aptamer-specific capture to form an exosome@fluorescence probe/aptamer sandwich structure. The one-to-many connection between exosomes and signal molecules and the aptamer-modified evanescent wave optical fiber detection platform reduced the detection limit of exosomes to 7.66 particles/mL, with a linear range of 47.5-4.75 × 10⁶ particles/mL. The entire detection process was simple, rapid, and real-time and lasted about 1 h while requiring no separation and purification. Additionally, this platform showed excellent surface regeneration capability and exhibited good performance during the analysis of tumor and non-tumor-derived exosomes.

Label-Free Electrochemical Detection of the Cancer Biomarker Platelet-Derived Growth Factor Receptor in Human Serum and Cancer Cells

Overexpression of the platelet-derived growth factor receptor (PDGFR) was already associated with the loss of p53 function as cancer progresses in lung, breast, and cervical cancers. Cancer biomarker detection has faced challenges and barriers due to various limitations, including a high limit of detection, low sensitivity, time-consuming techniques, and expensive equipment. Hence, the present investigation is designed to develop a cost-effective novel biosensor based on a charge-based affinity bait molecule to detect the PDGFR, thus overcoming the limitations and challenges with an immune technique based on antigen-antibody interactions. We employed EDC-NHS coupling between poly (diallyl dimethylammonium chloride) and poly(acrylic acid) to attach the multiwall carbon nanotube surface. As a result, we performed electrochemical PDGFR conversion sensing with a dynamic range of 1-10,000 ng/mL and a detection limit of 1.5 pg/mL, which is comparable to the best current results. The biosensor also displayed good selectivity, 2.51% repeatability (RSD, n = 5), and 30 days of stability. Our study provides a pathway for the design of diagnostic interfaces in biosystems, as well as the emergence of new sensor types based on ligand-receptor interactions.

Toward the Development of Rapid, Specific, and Sensitive Microfluidic Sensors: A Comprehensive Device Blueprint

Recent advances in nano/microfluidics have led to the miniaturization of surface-based chemical and biochemical sensors, with applications ranging from environmental monitoring to disease diagnostics. These systems rely on the detection of analytes flowing in a liquid sample, by exploiting their innate nature to react with specific receptors immobilized on the microchannel walls. The efficiency of these systems is defined by the cumulative effect of analyte detection speed, sensitivity, and specificity. In this perspective, we provide a fresh outlook on the use of important parameters obtained from well-characterized analytical models, by connecting the mass transport and reaction limits with the experimentally attainable limits of analyte detection efficiency. Specifically, we breakdown when and how the operational (e.g., flow rates, channel geometries, mode of detection, etc.) and molecular (e.g., receptor affinity and functionality) variables can be tailored to enhance the analyte detection time, analytical specificity, and sensitivity of the system (i.e., limit of detection). Finally, we present a simple yet cohesive blueprint for the development of high-efficiency surface-based microfluidic sensors for rapid, sensitive, and specific detection of chemical and biochemical analytes, pertinent to a variety of applications.

A CRISPR-based and post-amplification coupled SARS-CoV-2 detection with a portable evanescent wave biosensor

The continuing pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, which causes coronavirus disease 2019 (COVID-19), has spread globally and its reliable diagnosis is one of the foremost priorities for protecting public health. Herein a rapid (<1 h), easy-to-implement, and accurate CRISPR-based evanescent wave fluorescence biosensing platform for detection of SARS-CoV-2 is reported. The collateral effect of Cas13a is combined with a universal autonomous enzyme-free hybridization chain reaction (HCR) by designing a cleavage hairpin reporter, which is cleaved upon target recognition, and hence releasing the initiator sequence to trigger the downstream HCR circuits. Detection of HCR assemblies is accomplished by first adsorbing to the desthiobiotin-modified optical fiber, followed by fluorescence emission induced by an evanescent field. Three Cas13a crRNAs targeting the genes of S, N and Orf1ab of SARS-CoV-2 are programmed to specifically target SARS-CoV-2 or broadly detect related coronavirus strains, such as MERS-CoV and SARS-CoV. The HCR amplification coupled Cas13a-based biosensing platform is capable of rapid detection of SARS-CoV-2 with attomolar sensitivity. This method is further validated by adding target RNA of SARS-CoV-2 in negative oropharyngeal swabs. The good discrimination capability of this technique demonstrates its promising potential for point-of-care diagnosis of COVID-19.

Targeted Sub-Attomole Cancer Biomarker Detection Based on Phase Singularity 2D Nanomaterial-Enhanced Plasmonic Biosensor

A zero-reflection-induced phase singularity is achieved through precisely controlling the resonance characteristics using two-dimensional nanomaterials. An atomically thin nano-layer having a high absorption coefficient is exploited to enhance the zero-reflection dip, which has led to the subsequent phase singularity and thus a giant lateral position shift. We have improved the detection limit of low molecular weight molecules by more than three orders of magnitude compared to current state-of-art nanomaterial-enhanced plasmonic sensors. Detection of small cancer biomarkers with low molecular weight and a low concentration range has always been challenging yet urgent in many clinical applications such as diagnosing early-stage cancer, monitoring treatment and detecting relapse. Here, a highly enhanced plasmonic biosensor that can overcome this challenge is developed using atomically thin two-dimensional phase change nanomaterial. By precisely engineering the configuration with atomically thin materials, the phase singularity has been successfully achieved with a significantly enhanced lateral position shift effect. Based on our knowledge, it is the first experimental demonstration of a lateral position signal change > 340 μm at a sensing interface from all optical techniques. With this enhanced plasmonic effect, the detection limit has been experimentally demonstrated to be 10^-15 mol L^-1 for TNF-α cancer marker, which has been found in various human diseases including inflammatory diseases and different kinds of cancer. The as-reported novel integration of atomically thin Ge₂Sb₂Te₅ with plasmonic substrate, which results in a phase singularity and thus a giant lateral position shift, enables the detection of cancer markers with low molecular weight at femtomolar level. These results will definitely hold promising potential in biomedical application and clinical diagnostics.

Nanoscale Affinity Double Layer Overcomes the Poor Antimatrix Interference Capability of Aptamers

Poor antimatrix interference capability of aptamers is one of the major obstacles preventing their wide applications for real-sample detections. Here, we devise a multiple-function interface, denoted as a nanoscale affinity double layer (NADL), to overcome this bottleneck via in situ simultaneous target enrichment, purification, and detection. The NADL consists of an upper aptamer layer for target purification and sensing and a lower nanoscale solid-phase microextraction (SPME) layer for sample enrichment. The targets flowing through the NADL-functionalized surface are instantly million-fold enriched and purified by the sequential extraction of aptamer and SPME. The formation of the aptamer-target complex is greatly enhanced, enabling ultrasensitive detection of targets with minimized interference from the matrix. Taking the fiber-optic evanescent wave sensor as an example, we demonstrated the feasibility and generality of the NADL. The unprecedented detection of limits of 800, 4.8, 40, and 0.14 fM were, respectively, achieved for three representative small-molecule targets with distinct hydrophobicity (kanamycin A, sulfadimethoxine, and di-(2-ethylhexyl) phthalate) and protein target (human serum albumin), corresponding to 2500 to 3 × 10⁸-fold improvement compared to the sensors without the NADL. Our sensors also showed exceptionally high target specificity (>1000) and tunable dynamic ranges simply by manipulating the SPME layer. With these features comes the ability to directly detect targets in diluted environmental, food, and biological samples at concentrations all well below the tolerance limits.

A split aptamer (SPA)-based sandwich-type biosensor for facile and rapid detection of streptomycin

As antibiotic pollution is gaining prominence as a global issue, the demand for detection of streptomycin (STR), which is a widely used antibiotic with potential human health and ecological risks, has attracted increasing attention. Aptamer-based biosensors have been developed for the detection of STR in buffers and samples, however, the non-target signals due to the conformational variation of free aptamers possibly affect their sensitivity and stability. In this study, by introducing the STR-specific split aptamer (SPA), a sensitive evanescent wave fluorescent (EWF) biosensor is developed for the sandwich-type based detection of STR. The standard calibration curve obtained for STR has a detection limit of 33 nM with a linear range of 60-526 nM. This biosensor exhibited good selectivity, reliable reusability for at least 100 times measurements, and high recovery rates for spiked water samples; moreover, all detection steps are easy-to-operate and can be completed in 5 min. Therefore, it exhibits great promise for actual on-site environmental monitoring. Additionally, without introducing any other oligonucleotides or auxiliary materials, this SPA-based biosensing method shows potential as a simple, sensitive, and low-cost manner for the detection of other small molecular targets.

Binding enhancements of antibody functionalized natural and synthetic fibers

Development of low cost biosensing using convenient and environmentally benign materials is important for wide adoption and ultimately improved healthcare and sustainable development. Immobilized antibodies are often incorporated as an essential biorecognition element in point-of-care biosensors but these proteins are costly. We present a strategy of combining convenient and low-cost surface functionalization approaches for increasing the overall binding activity of antibody functionalized natural and synthetic fibers. We demonstrate a simple one-step in situ silica NP growth protocol for increasing the surface area available for functionalization on cotton and polyester fabrics as well as on nanoporous cellulose substrates. Comparing this effect with the widely adopted and low cost plant-based polyphenol coating to enhance antibody immobilization, we find that both approaches can similarly increase overall surface activity, and we illustrate conditions under which the two approaches can produce an additive effect. Furthermore, we introduce co-immobilization of antibodies with a sacrificial “steric helper” protein for further enhancing surface activities. In combination, several hundred percent higher activities compared to physical adsorption can be achieved while maintaining a low amount of antibodies used, thus paving a practical path towards low cost biosensing.

Cotton, nanoporous cellulose and polyester fabric surfaces are functionalized with combinations of in situ grown silica NPs, polyphenol coating, and protein co-immobilization to enhance surface area, antibody binding efficiency, and biosensing.

Waveguide-Based Fluorescent Immunosensor for the Simultaneous Detection of Carbofuran and 3-Hydroxy-Carbofuran

Carbofuran (CBF) is an efficient and broad-spectrum insecticide. As testing indicators for water quality and agricultural products, CBF and its metabolite 3-hydroxy-carbofuran (3-OH-CBF) are regulated by many countries. The detection of CBF and 3-OH-CBF is of great importance for the environment and human health. However, an immunosensor detection method for the simultaneous analysis of CBF and 3-OH-CBF remains unavailable. Herein, we report a waveguide-based fluorescent immunosensor for detecting CBF and 3-OH-CBF, synchronously. The immunosensor is based on a broad-spectrum monoclonal antibody with high binding affinity against CBF and 3-OH-CBF. The linear detection ranges for CBF and 3-OH-CBF are 0.29-2.69 and 0.12-4.59 μg/L, with limits of detection of 0.13 μg/L for CBF and 0.06 μg/L for 3-OH-CBF, respectively. The whole detection process for each cycle is approximately 30 min. The results show a good application prospect for the rapid detection of CBF and 3-OH-CBF in water or agricultural products.

Trypanosoma cruzi Virulence Factors for the Diagnosis of Chagas' Disease

trans-Sialidase and cruzipain are important virulence factors from Trypanosoma cruzi, the etiological agent of Chagas disease, that have highly antigenic domains in their structure and were reported as potential tools for diagnosis of the illness. The aim of the present study is to assess the possibility of using cruzipain and the catalytic domain of trans-sialidase in a Surface Plasmon Resonance-based immunosensor for the diagnosis of chronic Chagas disease. Immunoassays carried out with canine sera verified that cruzipain allows the detection of anti-Trypanosoma cruzi antibodies whereas recombinant trans-sialidase did not yield specific detections, due to the high dilutions of serum used in the immunoassays that hinder the possibility to sense the specific low titer antibodies. The developed cruzipain-based biosensor, whose price per assay is comparable to a commercial enzyme-linked immunosorbent assay (ELISA), was successfully applied for the rapid quantification of specific antibodies against Trypanosoma cruzi in fresh human sera showing an excellent agreement with ELISA.

Triple functional small-molecule-protein conjugate mediated optical biosensor for quantification of estrogenic activities in water samples

Establishing biosensors to map a comprehensive picture of potential estrogen-active chemicals remains challenging and must be addressed. Herein, we describe an estrogen receptor (ER)-based evanescent wave fluorescent biosensor by using a triple functional small-molecule-protein conjugate as a signal probe for the determination of estrogenic activities in water samples. The signal probe, consisting of a Cy5.5-labelled streptavidin (STV) moiety and a 17β-estradiol (E₂) moiety, acts simultaneously as signal conversion, signal recognition and signal report elements. When xenoestrogens compete with the E₂ moiety of conjugate in binding to the ER, the unbound conjugates are released, and their STV moiety binds with desthiobiotin (DTB) modified on the optical fiber via the STV-DTB affinity interactions. Signal probe detection is accomplished by fluorescence emission induced by an evanescent field, which positively relates with the estrogenic activities in samples. Quantification of estrogenic activity expressed as E₂ equivalent concentration (EEQ) can be achieved with a detection limit of 1.05 μg/L EEQ by using three times standard deviation of the mean blank values and a linear calibration range from 20.8 to 476.7 μg/L EEQ. The optical fiber system is robust enough for hundreds of sensing cycles. The biosensor-based determination of estrogenic activities in wastewater samples obtained from a full-scale wastewater treatment plant is consistent with that measured by the two-hybrid recombinant yeast bioassay.

Multitag-Regulated Cascade Reaction: A Generalizable Ultrasensitive MicroRNA Biosensing Approach for Cancer Prognosis

Ultrasensitive PCR-free microRNA (miR) analysis based on biosensors with enzyme-free nucleic acid amplification and reusable surface has great clinical significance in cancer prognosis. However, building such a biosensing strategy has long been challenging due to uncontrollable miR-triggered cascade amplifiers and insufficient sensing surface regeneration capability. To meet the challenge, for the first time, a general approach, named enzyme-free multitag-regulated cascade reaction (MCR), is developed to fabricate reliable trace miR biosensors. As a proof of concept, miR let-7a is detected on an evanescent wave fluorescent optical-fiber biosensing platform. The size and morphology of well-formed MCR assemblies (∼1 μm in length) are characterized by atomic force microscopy. This MCR method achieves a 30 000-fold improved sensitivity (detection limit 0.8 fM) compared to the MCR-free system and can detect abnormal urinary miR levels in lung cancer patients. Moreover, the biosensor is robust enough to be reused for over 100 cycles, which greatly reduces the cost of single detection. In sum, MCR is developed as a generalizable ultrasensitive miR biosensing approach for cancer prognosis, which opens a broad field for facile enzyme-free biosensing applications by nucleic acid assembling regulation.

Ultraselective antibiotic sensing with complementary strand DNA assisted aptamer/MoS2 field-effect transistors

Although aptamer has been demonstrated as an important probe for antibiotic determination, the selective sensing of different antibiotics is still a challenge due to their structure similarities and wide folding degrees of aptamer. Herein, a field-effect transistor using MoS₂ nanosheet as the channel and an aptamer DNA (APT) with its configuration shaped by a complementary strand DNA (CS) is employed for kanamycin (KAN) determination. This probe structure contributes to an enhanced selectivity and reliability with reduced device-to-device variations. This MoS₂/APT/CS sensor shows time-dependent performance in antibiotic sensing. Prolonged detection time (20 s-300 s) leads to an enhanced sensitivity (1.85-4.43 M^-1) and a lower limit of detection (1.06-0.66 nM), while a shorter detection time leads to a broader linear working range. A new sensing mechanism relying on charge release from probe is proposed, which is based on the "replacement reaction" between KAN and APT-CS. This sensor exhibits an extremely high selectivity (selectivity coefficient of 12.8) to kanamycin over other antibiotics including streptomycin, tobramycin, amoxicillin, ciprofloxacin and chloramphenicol. This work demonstrates the merits of probe engineering in label-free antibiotic detection with FET sensor, which presents significant promises in sensitive and selective chemical and biological sensing.

Visualization and colorimetric determination of clenbuterol in pork by using magnetic beads modified with aptamer and complementary DNA as capture probes, and G-quadruplex/hemin and DNA antibody on the metal-organic framework MIL-101(Fe) acting as a peroxidase mimic

A visualization strategy is described for the detection of clenbuterol (CLB). It is using of antibody against dsDNA and G-quadruplex/hemin labeled on a metal organic framework of type MIL-101(Fe) (G-quadruplex/hemin-anti-DNA/MIL-101) acting as a peroxidase mimetic, and magnetic beads modified with aptamer and complementary DNA (MB/Apt-cDNA) as capture probes. The detection reagent was prepared via the reactions between the double stranded DNA (Apt-cDNA) in capture probes and anti-DNA in peroxidase mimetic. In the presence of CLB, the aptamer on the magnetic beads preferentially binds CLB, and the peroxidase mimetic is released to the supernatant after magnetic separation. The released peroxidase mimetic can catalyze the TMB/H₂O₂ chromogenic system under mild conditions. This leads to the development of a blue-green coloration whose absorbance is measured at 650 nm. The detection limit is as low as 34 fM of CLB. The method was applied to the determination of CLB in pork samples and gave results that were consistent with data obtained with an ELISA kit. Graphical abstract A visualization strategy is described for the detection of clenbuterol. The selectivity of detection system for clenbuterol is excellent compared with other interferents. The method was applied to the determination of CLB in pork samples.

Direct immobilization of sugar probes on bovine serum albumin-coated gold substrate for the development of glycan biosensors

Glycan biosensors based on surface plasmon resonance (SPR) spectroscopy have attracted a great deal of interest due to their potential applications in numerous biological and biomedical fields. Controlled immobilization of sugar probes on a gold substrate is believed to be critical for the performance of these SPR biosensors. In this regard, herein the authors report a direct coupling of mannose probes with bovine serum albumin (BSA) layer on the gold substrate via a squaric acid-mediated reaction under mild conditions, in which the BSA layer provides not only reactive amine groups but also a nonfouling surface property. SPR measurements show that the resultant biosensor with an appropriate amount of mannose probes exhibits high affinity to its corresponding lectin (i.e., concanavalin A) and at the same time could resist nonspecific adsorption of other lectins. The limit of detection of the current SPR biosensor is 1.9 nM. Thus, the squaric acid-mediated immobilization strategy appears to be effective and useful for the fabrication of bioanalytical devices.

Nucleic acid functionalized fiber optic probes for sensing in evanescent wave: optimization and application

Nucleic acid functionalized evanescent wave fiber optic (EWFO) biosensors have attracted much attention due to their remarkable advantages in both device configuration and sensing performance. One critical technique in EWFO biosensor fabrication is its surface modification, which requires (1) minimal nonspecific adsorption and (2) high-quality DNA immobilization to guarantee satisfactory sensing performances. Focusing on these two requirements, a series of optimizations have been conducted in this work to develop reliable DNA-functionalized EWFO probes. Firstly, the surface planeness of EWFO probes were found to be greatly improved by a novel HF/HNO₃ mixture etching solution. Both atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were conducted to investigate the morphological structures and surface chemical compositions. Besides, EWFO sensing performances adopting moderate immobilization of irrelevant DNA were investigated for optimization purposes. Furthermore, a split aptamer based sandwich-type EWFO sensor was developed using adenosine (Ade) as the model target (LOD = 25 μM). To the best of our knowledge, this study is the first case to focus on the optimization of etching solution compositions in the fabrication of combination tapered fibers, which provides experimental basis for the understanding of the silica-etching mechanism using HF/HNO₃ mixture solution and may further inspire related researches.

Reliable DNA-functionalized optic probes for sensing in evanescent wave have been developed based a series of optimizations on the etching solution and immobilization chemistry.

Femtomolar Detection by Nanocoated Fiber Label-Free Biosensors

The advent of optical fiber-based biosensors combined with that of nanotechnologies has provided an opportunity for developing in situ, portable, lightweight, versatile, and high-performance optical sensing platforms. We report on the generation of lossy mode resonances by the deposition of nanometer-thick metal oxide films on optical fibers, which makes it possible to measure precisely and accurately the changes in optical properties of the fiber-surrounding medium with very high sensitivity compared to other technology platforms, such as long period gratings or surface plasmon resonances, the gold standard in label-free and real-time biomolecular interaction analysis. This property, combined with the application of specialty structures such as D-shaped fibers, permits enhancing the light-matter interaction. SEM and TEM imaging together with X-EDS tool have been utilized to characterize the two films used, i.e., indium tin oxide and tin dioxide. Moreover, the experimental transmission spectra obtained after the deposition of the nanocoatings have been numerically corroborated by means of wave propagation methods. With the use of a conventional wavelength interrogation system and ad hoc developed microfluidics, the shift of the lossy mode resonance can be reliably recorded in response to very low analyte concentrations. Repeated experiments confirm a big leap in performance thanks to the capability to detect femtomolar concentrations in human serum, improving the detection limit by 3 orders of magnitude when compared with other fiber-based configurations. The biosensor has been regenerated several times by injecting sodium dodecyl sulfate, which proves the capability of sensor to be reused.

Sensitive and simultaneous surface plasmon resonance detection of free and p53-bound MDM2 proteins from human sarcomas

Murine double minute 2 (MDM2) is an oncoprotein mediating the degradation of the tumor suppressor p53 protein. The physiological levels of MDM2 protein are closely related to malignant transformation and tumor growth. In this work, the simultaneous and label-free determination of free and p53-bound MDM2 proteins from sarcoma tissue extracts was conducted using a dual-channel surface plasmon resonance (SPR) instrument. Free MDM2 protein was measured in one fluidic channel covered with the consensus double-stranded (ds)-DNA/p53 conjugate, while MDM2 bound to p53 was captured by the consensus ds-DNA immobilized onto the other channel. To achieve higher sensitivity and to confirm specificity, an MDM2-specific monoclonal antibody (2A10) was used to recognize both the free and p53-bound MDM2 proteins. The resultant method afforded a detection limit of 0.55 pM of MDM2. The amenability of the method to the analysis of free and p53-bound MDM2 proteins was demonstrated for normal and sarcoma tissue extracts from three patients. Our data reveal that both free and total MDM2 (free and bound forms combined) proteins from sarcoma tissue extracts are of much higher concentrations than those from normal tissue extracts and the p53-bound MDM2 protein only constitutes a small fraction of the total MDM2 concentration. In comparison with enzyme-linked immunosorbent assay (ELISA), the proposed method possesses higher sensitivity, is more cost-effective, and is capable of determining free and p53-bound MDM2 proteins in clinical samples.

Chimeric DNA/LNA-based biosensor for the rapid detection of African swine fever virus

African swine fever (ASF) virus is a DNA virus responsible for a severe haemorrhagic fever in pigs, which (still in the absence of vaccination strategies) results in high mortality rates. Herein, we present a biosensor-based method for the detection of ASF viral DNA in the blood of pigs. The biosensor exploits a single-strand DNA probe with locked nucleic acid nucleotides (LNA) substitutions as the complementary recognition element for the conserved region of vp72 gene of ASF virus. The biosensor was calibrated using qPCR-quantified ASF viral DNA extracted from the blood of pigs experimentally infected with the virulent Italian isolate 49/08, genotype I. Globally, the proposed biosensor showed good sensitivity and specificity, with the limits of detection (LOD) and quantification (LOQ) being 178 and 245 copies/μL of genomic ASF viral DNA, respectively. The reversible nature of the interaction between the DNA/LNA probe and the target DNA sequence granted multiple rapid analyses, with up to 40 analyses per single surface possible, and a single test requiring approximately 5 min. When applied to non-amplified DNA extracts from the blood of field-infected pigs, the assay discriminated between ASFV-infected and ASFV non-infected animals, and allowed the rapid quantification of ASF viral DNA, with values falling in the range 373-1058 copies/μL of genomic ASFV DNA. In this range, excellent correlation was observed between the results of this biosensor and OIE-approved qPCR. This method represents a promising screening assay for preliminary ASF diagnosis, having the major advantages in the relative rapidity, ease-of-use, the reusability of the sensing surface, and low cost per single test.

An Optical Biosensor-Based Quantification of the Microcystin Synthetase A Gene: Early Warning of Toxic Cyanobacterial Blooming

The monitoring and control of toxic cyanobacterial strains, which can produce microcystins, is critical to protect human and ecological health. We herein reported an optical-biosensor-based quantification of the microcystin synthetase A (mcyA) gene so as to discriminate microcystin-producing strains from nonproducing strains. In this assay, the mcyA-specific ssDNA probes were designed in silico with an on-line tool and then synthesized to be covalently immobilized on an optical-fiber surface. Production of fluorescently modified target DNA fragment amplicons was accomplished through the use of Cy5-tagged deoxycytidine triphosphates (dCTPs) in the polymerase chain reaction (PCR) method, which resulted in copies with internally labeled multiple sites per DNA molecule and delivered great sensitivity. With a facile surface-based hybridization process, the PCR amplicons were captured on the optical-fiber surface and were induced by an evanescent-wave field into fluorescence emission. Under the optimum conditions, the detection limit was found to be 10 pM (S/N ratio = 3) and equaled 10³ gene copies/mL. The assay was triumphantly demonstrated for PCR amplicons of mcyA detection and showed satisfactory stability and reproducibility. Moreover, the sensing system exhibited excellent selectivity with quantitative spike recoveries from 87 to 102% for M. aeruginosa species in the mixed samples. There results confirmed that the method would serve as an accurate, cost-effective, and rapid technique for in-field testing of toxic Microcystis sp. in water, giving early information for water quality monitoring against microcystin-producing cyanobacteria.

Label-free electrochemical immunosensor for ultrasensitive detection of neuron-specific enolase based on enzyme-free catalytic amplification

Enzyme-free catalytic amplification is of great significance for sensitive label-free electrochemical immunosensors. In this study, an enzyme-free catalytic amplification based label-free amperometric immunosensor was developed for sensitive detection of neuron-specific enolase (NSE) by use of a AuPd nanoparticle-multiwalled carbon nanotube (AuPd-MWCNT) composite, ferrocenecarboxaldehyde (Fc-CHO), and chitosan hybrid hydrogel. The intrinsic virtues of chitosan not only resulted in bioactivity of the attached antibodies and made the other component of the immunosensor easier to fix on the electrode, but also imparted abundant binding sites to the hydrogel to condense Fc-CHO to achieve the initial signal amplification. Fc-CHO, which served as an electroactive species to generate a redox response, also exhibits excellent electrocatalytic activity toward H₂O₂. AuPd-MWCNT composite, with enhanced peroxidase-like catalytic activity, could catalyze H₂O₂ to accelerate electron transfer. When H₂O₂ was present in the detection solution, synergetic catalysis of Fc-CHO and AuPd-MWCNT composite toward H₂O₂ was achieved, thus realizing enzyme-free signal amplification. On the basis of this enzyme-free signal amplification, the electrochemical immunosensing platform provided a wide linear range from 1 pg mL^-1 to 100 ng mL^-1, a low detection limit of 0.483 pg mL^-1, and high sensitivity of 7.22 μA (log₁₀ C _NSE)^-1. Moreover, the immunosensor showed enormous potential in clinical application. Graphical abstract An enzyme-free catalytic amplification based label-free amperometric immunosensor was developed for sensitive detection of neuron-specific enolase (NSE) by use of a AuPd nanoparticle-multiwalled carbon nanotube (MWCNT) composite, ferrocenecarboxaldehyde (Fc-CHO), and chitosan (CS) hybrid hydrogel. BSA bovine serum albumin, GA glutaraldehyde, SWV square wave voltammetry.

Free-Energy-Driven Lock/Open Assembly-Based Optical DNA Sensor for Cancer-Related microRNA Detection with a Shortened Time-to-Result

Quantification of cancer biomarker microRNAs (miRs) by exquisitely designed biosensors with a short time-to-result is of great clinical significance. With immobilized capture probes (CPs) and fluorescent-labeled signal probes (SPs), surface-involved sandwich-type (SST) biosensors serve as powerful tools for rapid, highly sensitive, and selective detection of miR in complex matrices as opposed to the conventional techniques. One key challenge for such SST biosensors is the existence of false-negative signals when the amount of miRs exceeds SPs in solution phase for a surface with a limited number of CP. To meet this challenge, a dynamic lock/open DNA assembly was designed to rationally program the pathway for miR/SP hybrids. Based on secondary structure analysis and free-energy assessment, a "locker" strand that partially hybridizes with target miR by two separated short arms was designed to stabilize target miR, preventing possible false-negative signals. The strategy was demonstrated on a fiber-based fluorescent DNA-sensing platform. CP/miR/SP sandwiches formed on the fiber surface would generate fluorescent signals for quantitative analysis. The developed SST biosensor was able to detect miR Hsa let-7a with a detection limit of 24 pM. The applicability of this free-energy-driven lock/open assembly-based optical DNA sensor was further confirmed with spiked human urine and serum samples.