Nanoplasmonic Biosensor Research Articles

Label-free nanoplasmonic sensing of tumor-associate autoantibodies for early diagnosis of colorectal cancer

Colorectal cancer is treatable and curable when detected at early stages. However there is a lack of less invasive and more specific screening and diagnosis methods which would facilitate its prompt identification. Blood circulating autoantibodies which are immediately produced by the immune system at tumor appearance have become valuable biomarkers for preclinical diagnosis of cancer. In this work, we present the rapid and label-free detection of colorectal cancer autoantibodies directly in blood serum or plasma using a recently developed nanoplasmonic biosensor. Our nanoplasmonic device offers sensitive and real-time quantification of autoantibodies with excellent selectivity and reproducibility, achieving limits of detection around 1 nM (150–160 ng mL−1). A preliminary evaluation of clinical samples of colorectal cancer patients has shown good correlation with ELISA. These results demonstrate the reliability of the nanobiosensor strategy and pave the way towards the achievement of a sensitive diagnostic tool for early detection of colorectal cancer.

Enzyme-coupled nanoplasmonic biosensing of cancer markers in human serum

As the use of biosensors for early in-vitro diagnosis of malignant diseases has expanded, issues associated with ultra-sensitivity and wide dynamic range have become paramount. In this study, we designed a sub-zeptomolar sensor for detecting the alpha-feto protein (AFP) that utilizes localized surface plasmon resonance (LSPR) assisted by bio-catalytic reaction and a self-controlled detection scheme. A gold nanodot array (GNA), serving as a plasmonic material, was fabricated using an improved UV nanoimprint lithography (NIL) method that employs a sacrificial layer. In the new approach, LSPR observation is highly stable because it employs a back reflection mode, which avoids passing the signal through the sample solution. An enzyme-precipitation reaction was conducted on the AFP antigen-antibody complex on the surface of the gold nanodot (nano-ELISA) using a procedure that was described previously. To extend the AFP detection limit below femtomolar concentrations, a scheme involving self-controlled detection was employed to lower the limit. In this method, the sample including the target simultaneously plays the role of both sample and negative control. Using this scheme, AFP can be detected at concentrations as low as 14 aM (0.7 zeptomole in 50μL serum) and with the wide dynamic range of 10fgmL−1–10ngmL−1. Importantly, the new method provides a platform for studying and monitoring interactions between biochemically active substances that are present in very low concentrations. Finally, the general strategy used to design the detection method can be easily adapted to the ultra-sensitive detection of other biomarkers and pathogens.

Electrophoresis-enhanced nanoplasmonic biosensor with nanocup arrays for protease detection in point-of-care diagnostics

Electrophoresis-enhanced nanoplasmonic biosensor with nanocup arrays for protease detection in point-of-care diagnostics

Orthogonal chemical functionalization of patterned gold on silica surfaces.

Single-step orthogonal chemical functionalization procedures have been developed with patterned gold on silica surfaces. Different combinations of a silane and a thiol were simultaneously deposited on a gold/silica heterogeneous substrate. The orthogonality of the functionalization (i.e., selective grafting of the thiol on the gold areas and the silane on the silica) was demonstrated by X-ray photoelectron spectroscopy (XPS) as well as time-of-flight secondary ion mass spectrometry (ToF–SIMS) mapping. The orthogonal functionalization was used to immobilize proteins onto gold nanostructures on a silica substrate, as demonstrated by atomic force microscopy (AFM). These results are especially promising in the development of future biosensors where the selective anchoring of target molecules onto nanostructured transducers (e.g., nanoplasmonic biosensors) is a major challenge.

Nanoplasmonic biosensors: current perspectives

Recent advances in nanotechnology and nanofabrication have helped develop a wide variety of nanostructured platforms for use as nanoplasmonic biosensors. These can either be in solution phase or be confined on a substrate in the form of metallic nanofilms or periodic arrays. Plasmonic properties of these nanostructures depend on the size, shape, position, orientation, etc, and can be altered by interaction between probe and target species on the metal surfaces. This property of nanostructures has been exploited in refractometric nanoplasmonic biosen- sors, surface-enhanced Raman spectroscopy-based biosensors, plasmon-enhanced fluorescence biosensors, etc. These nanoplasmonic biosensors are employed in diverse areas such as clinical diagnosis, biosecurity, food, and environmental monitoring. Among these, clinical diagnosis has attracted the most research and commercial interest. Nanoplasmonic biosensors can detect disease biomarkers using highly specific and selective biological recognition elements on the nanostructured surfaces. Many excellent reviews exist in this area that trace the developments over the past 3 decades. This review focuses on some of the more recent studies on the detec- tion of various disease biomarkers through nanoplasmonic biosensors. In the process, we have

MLFMA-MoM for Solving the Scattering of Densely Packed Plasmonic Nanoparticle Assemblies

In this paper, we present a judicious combination of two renowned surface integral equation (SIE)-based techniques, namely, the multilevel fast multipole algorithm (MLFMA) and the method of moments (MoM), which synergize into a hybrid method that allows to address the analysis of large densely packed particle assemblies in an efficient and accurate way. This hybridization takes advantage of the repetition pattern inherent to these kinds of structures. Basically, the repeated self-coupling problems are squarely solved throughout the factorization of their MoM impedance matrix, whereas the cross-couplings through the surrounding medium are expedited via the MLFMA in the framework of a global iterative scheme. Some results are presented here to demonstrate the suitability of the proposed hybrid method to address large-scale nanoparticle arrays in the framework of nanoplasmonic biosensing applications.

Optimizing Nanoplasmonic Biosensor Sensitivity with Orientated Single Domain Antibodies.

Localized surface plasmon resonance (LSPR) spectroscopy and imaging are emerging biosensor technologies which tout label-free biomolecule detection at the nanoscale and ease of integration with standard microscopy setups. The applicability of these techniques can be limited by the restrictions that surface-conjugated ligands must be both sufficiently small and orientated to meet analyte sensitivity requirements. We demonstrate that orientated single domain antibodies (sdAb) can optimize nanoplasmonic sensitivity by comparing three anti-ricin sdAb constructs to biotin-neutravidin, a model system for small and highly orientated ligand studies. LSPR imaging of electrostatically orientated sdAb exhibited a ricin sensitivity equivalent to that of the biotinylated LSPR biosensors for neutravidin. These results, combined with the facts that sdAb are highly stable and readily produced in bacteria and yeast, build a compelling case for the increased utilization of sdAbs in nanoplasmonic applications.Electronic supplementary materialThe online version of this article (doi:10.1007/s11468-015-9969-3) contains supplementary material, which is available to authorized users.

Multiplex serum cytokine immunoassay using nanoplasmonic biosensor microarrays.

Precise monitoring of the rapidly changing immune status during the course of a disease requires multiplex analysis of cytokines from frequently sampled human blood. However, the current lack of rapid, multiplex, and low volume assays makes immune monitoring for clinical decision-making (e.g., critically ill patients) impractical. Without such assays, immune monitoring is even virtually impossible for infants and neonates with infectious diseases and/or immune mediated disorders as access to their blood in large quantities is prohibited. Localized surface plasmon resonance (LSPR)-based microfluidic optical biosensing is a promising approach to fill this technical gap as it could potentially permit real-time refractometric detection of biomolecular binding on a metallic nanoparticle surface and sensor miniaturization, both leading to rapid and sample-sparing analyte analysis. Despite this promise, practical implementation of such a microfluidic assay for cytokine biomarker detection in serum samples has not been established primarily due to the limited sensitivity of LSPR biosensing. Here, we developed a high-throughput, label-free, multiarrayed LSPR optical biosensor device with 480 nanoplasmonic sensing spots in microfluidic channel arrays and demonstrated parallel multiplex immunoassays of six cytokines in a complex serum matrix on a single device chip while overcoming technical limitations. The device was fabricated using easy-to-implement, one-step microfluidic patterning and antibody conjugation of gold nanorods (AuNRs). When scanning the scattering light intensity across the microarrays of AuNR ensembles with dark-field imaging optics, our LSPR biosensing technique allowed for high-sensitivity quantitative cytokine measurements at concentrations down to 5-20 pg/mL from a 1 μL serum sample. Using the nanoplasmonic biosensor microarray device, we demonstrated the ability to monitor the inflammatory responses of infants following cardiopulmonary bypass (CPB) surgery through tracking the time-course variations of their serum cytokines. The whole parallel on-chip assays, which involved the loading, incubation, and washing of samples and reagents, and 10-fold replicated multianalyte detection for each sample using the entire biosensor arrays, were completed within 40 min.

Contribution of temperature to deformation of adsorbed vesicles studied by nanoplasmonic biosensing.

With increasing temperature, biological macromolecules and nanometer-sized aggregates typically undergo complex and poorly understood reconfigurations, especially in the adsorbed state. Herein, we demonstrate the strong potential of using localized surface plasmon resonance (LSPR) sensors to address challenging questions related to this topic. By employing an LSPR-based gold nanodisk array platform, we have studied the adsorption of sub-100-nm diameter 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipid vesicles on titanium oxide at two temperatures, 23 and 50 °C. Inside this temperature range, DPPC lipid vesicles undergo the gel-to-fluid phase transition accompanied by membrane area expansion, while DOPC lipid vesicles remain in the fluid-phase state. To interpret the corresponding measurement results, we have derived general equations describing the effect of deformation of adsorbed vesicles on the LSPR signal. At the two temperatures, the shape of adsorbed DPPC lipid vesicles on titanium oxide remains nearly equivalent, while DOPC lipid vesicles become less deformed at higher temperature. Adsorption and rupture of DPPC lipid vesicles on silicon oxide were also studied for comparison. In contrast to the results obtained on titanium oxide, adsorbed vesicles on silicon oxide become more deformed at higher temperature. Collectively, the findings demonstrate that increasing temperature may ultimately promote, hinder, or have negligible effect on the deformation of adsorbed vesicles. The physics behind these observations is discussed, and helps to clarify the interplay of various, often hidden, factors involved in adsorption of biological macromolecules at interfaces.

Gold nanostar based biosensor detects epigenetic alterations on promoter of real cells

Epigenetic changes, particularly in cancer suppressor genes, are novel biomarkers for cancer diagnostics and therapeutics. However, epigenetic studies should not only provide an estimation of the amount of 5-methylcytosine, but also examine the presence of epigenetic proteins to reveal the complete epigenetic alterations for downstream molecular process. The challenge of natural epigenetics is to unveil key factors of epigenetics in one assay, containing low concentrations. This would be valuable for the monitoring of early-stage cancer. On the basic of the nanoplasmonic biosensor, here we report a sensitive sensor to study epigenetics of DNA promoter. The results show detection limit for dual epigenetic biomarkers methyl-CpG group and methyl-CpG binding domain protein 2 (MBD2) are one 5-methylcytosine molecule and 125fM MBD2. Moreover, DNA structure bending, steric competition under interaction of epigenetic proteins and transcription factors; and epigenetics-mediated suppression of transcription are observed during epigenetic alterations. This study provides a platform for full story of epigenetics, as compared with that of methylcytosine-based techniques only.

Highly sensitive dendrimer-based nanoplasmonic biosensor for drug allergy diagnosis

A label-free biosensing strategy for amoxicillin (AX) allergy diagnosis based on the combination of novel dendrimer-based conjugates and a recently developed nanoplasmonic sensor technology is reported. Gold nanodisks were functionalized with a custom-designed thiol-ending-polyamido-based dendron (d-BAPAD) peripherally decorated with amoxicilloyl (AXO) groups (d-BAPAD–AXO) in order to detect specific IgE generated in patient's serum against this antibiotic during an allergy outbreak. This innovative strategy, which follows a simple one-step immobilization procedure, shows exceptional results in terms of sensitivity and robustness, leading to a highly-reproducible and long-term stable surface which allows achieving extremely low limits of detection. Moreover, the viability of this biosensor approach to analyze human biological samples has been demonstrated by directly analyzing and quantifying specific anti-AX antibodies in patient's serum without any sample pretreatment. An excellent limit of detection (LoD) of 0.6ng/mL (i.e. 0.25kU/L) has been achieved in the evaluation of clinical samples evidencing the potential of our nanoplasmonic biosensor as an advanced diagnostic tool to quickly identify allergic patients. The results have been compared and validated with a conventional clinical immunofluorescence assay (ImmunoCAP test), confirming an excellent correlation between both techniques. The combination of a novel compact nanoplasmonic platform and a dendrimer-based strategy provides a highly sensitive label free biosensor approach with over two times better detectability than conventional SPR. Both the biosensor device and the carrier structure hold great potential in clinical diagnosis for biomarker analysis in whole serum samples and other human biological samples.

Nanoplasmonic biosensor: detection and amplification of dual bio-signatures of circulating tumor DNA.

Circulating tumor DNA (ctDNA) bearing tumor-specific mutation and methylation are promising biomarkers for noninvasive cancer assessment. However, existing methods for ctDNA detection are restricted to genetic mutations. Recently, nanoplasmonics has emerged as a platform for one-step dual detection with high sensitivity and specificity. Here we present a strategy for ultrasensitive detection of tumor-specific mutations (E542K and E545K) and methylation of ctDNA of PIK3CA gene based on localized surface plasmon resonance (LSPR) and the coupling plasmon mode of gold nanoparticles (AuNPs). Peptide nucleic acids (PNA) is used as a probe to capture and enrich the 69-bp PIK3CA ctDNA. The exposure of PNA-probed AuNPs to 200 fM ctDNA generates LSPR-peak shift of 4.3 nm, corresponding to the primary response. Immunogold colloids are exploited as methylation detectors and plasmon coupling based enhancement for secondary response. LSPR-peak shifted from 4.3 nm to 11.4 nm upon the immunogold colloids binding to two methylcytosines (mCpG), which is an approximately 107% increase, compared to that of the primary response. This enhancement leads to four times (~50 fM) improvement of sensitivity and because of two mCpG sites, ctDNA was detected. These results demonstrate that the sensor can simultaneously detect the hot-spot mutation and epigenetic changes on the ctDNA. Promisingly, other specific-tumor mutants and epigenetic changes can be detected at low concentration with this platform.

Controlling lipid membrane architecture for tunable nanoplasmonic biosensing.

Tunable nanoplasmonic biosensing for lipid and protein applications is reported based on controlling lipid membrane architecture on surfaces. The interaction of a peptide with lipid membranes is highly sensitive to the membrane architecture on top of plasmonic nanodisks, and the measurement response varies in a manner which is consistent with the surrounding lipid environment.

Nanoplasmonic biosensing for soft matter adsorption: kinetics of lipid vesicle attachment and shape deformation.

An indirect nanoplasmonic sensing platform is reported for investigating the kinetics of attachment and shape deformation associated with lipid vesicle adsorption onto a titanium oxide-coated substrate. The localized surface plasmon resonance (LSPR) originates from embedded gold nanodisks and is highly sensitive to the local lipid environment. To interpret the corresponding results, we have extended treatments of diffusion-limited adsorption kinetics and adsorbate-related LSPR physics, identified the expected scaling laws for the LSPR-tracked kinetics measured at different lipid concentrations and/or nanometer-scale vesicle sizes in the case when vesicle deformation is negligible, and scrutinized experimental deviations accordingly. After adsorption, the smallest 58 nm diameter vesicles were found to maintain shape on the time scale of adsorption at high lipid concentrations in solution, and shape deformation became more appreciable at lower lipid concentrations. Higher saturation coverage was observed with increasing lipid concentration, which is attributed to the difference in relative time scales of vesicle attachment and deformation. For larger vesicles between 80 and 160 nm diameter, deviations associated with their shape deformation and correlations with the location of gold nanodisks became more apparent at moderate and high coverages. Taken together, the results obtained support that the quantitative measurement capabilities of nanoplasmonic biosensing should be considered for applications demanding highly surface-sensitive characterization of soft matter adsorption and related phenomena at liquid-solid interfaces.

Single gold nanoplasmonic sensor for clinical cancer diagnosis based on specific interaction between nucleic acids and protein

Plasmonic nanomaterials reveal noble optical properties for next-generation biosensors. Nanoplasmonic biosensors have become simple, sensitive, smart, and consistent with advanced healthcare programs requirements. Notably, an individual nanoparticle analysis can yield unique target information, based on which the next-generation biosensor is revolutionary for end-point detection (single or multiplex), and can be functionally extended to biological phenomena monitoring. Here, we present a single nanoplasmonic sensing technology based on localized surface plasmon resonance for label-free and real-time detection of highly reliable cancer markers (mutant gene and telomerase) in clinical samples. The sensor specifically detects mutant DNA, and can detect telomerase from as few as 10 HeLa cells. This approach can be easily translated to detect other pathological targets with high sensitivity and specificity, and monitor key interactions between biomolecules such as nucleic acids and proteins during disease development in real time. This system has great potential to be further developed for on-chip and simultaneous analysis of multiple targets and interactions.

A route to low-cost nanoplasmonic biosensor integrated with optofluidic-portable platform

The optofluidic nanoplasmonic biosensors could offer label-free monitoring of biomolecular interactions in real-time with the low consumption of the sample, which stimulate researchers’ tremendous interest. To meet the need of the laboratory and clinic testing, the protocols of fabricating nanoplasmonic biosensor and testing processes were detailedly described, which is simple and low-cost. The photolithography, electron beam evaporation, annealing and bonding were applied to fabricate the nanoplasmonic biosensor which integrated with microfluidics on an optofluidic-portable platform. The 9 kinds of samples with different reflective index and antigen/antibody system were utilized to characterize the developed nanoplasmonic biosensor. Meanwhile, the biomarker of the liver cancer also was tested in situ and real time by the optofluidic platform. The detected concentration of the liver cancer antigen and antibody reached 45.24ng/ml and 25ng/ml, respectively. This method could improve the diagnosing accuracy in the liver cancer early stage or other serious diseases.

Single step nanoplasmonic immunoassay for the measurement of protein biomarkers.

A nanoplasmonic biosensor for highly-sensitive, single-step detection of protein biomarkers is presented. The principle is based on the utilization of the optical scattering properties of gold nanorods (GNRs) conjugated to bio-recognition molecules. The nanoplasmonic properties of the GNRs were utilized to detect proteins using near-infrared light interferometry. We show that the antibody-conjugated GNRs can specifically bind to our model analyte, Glucose Transporter-1 (Glut-1). The signal intensity of back-scattered light from the GNRs bound after incubation, correlated well to the Glut-1 concentration as per the calibration curve. The detection range using this nanoplasmonic immunoassay ranges from 10 ng/mL to 1 ug/mL for Glut-1. The minimal detectable concentration based on the lowest discernable concentration from zero is 10 ng/mL. This nanoplasmonic immunoassay can act as a simple, selective, sensitive strategy for effective disease diagnosis. It offers advantages such as wide detection range, increased speed of analysis (due to fewer incubation/washing steps), and no label development as compared to traditional immunoassay techniques. Our future goal is to incorporate this detection strategy onto a microfluidic platform to be used as a point-of-care diagnostic tool.

All-thermoplastic nanoplasmonic microfluidic device for transmission SPR biosensing

Early and accurate disease diagnosis still remains a major challenge in clinical settings. Biomarkers could potentially provide useful tools for the detection and monitoring of disease progression, treatment safety and efficacy. Recent years have witnessed prodigious advancement in biosensor development with research directed towards rapid, real-time, label-free and sensitive biomarker detection. Among emerging techniques, nanoplasmonic biosensors pose tremendous potential to accelerate clinical diagnosis with real-time multiplexed analysis, rapid and miniaturized assays, low sample consumption and high sensitivity. In order to translate these technologies from the proof-of-principle concept level to point of care clinical diagnosis, integrated, portable devices having small footprint cartridges that house low-cost disposable consumables are sought. Towards this goal, we developed an all-polymeric nanoplasmonic microfluidic (NMF) transmission surface plasmon resonance (SPR) biosensor. The device was fabricated in thermoplastics using a simple, single step and cost-effective hot embossing technique amenable to mass production. The novel 3D hierarchical mold fabrication process enabled monolithic integration of blazed nanogratings within the detection chambers of a multichannel microfluidic system. Consequently, a single hard thermoplastic bottom substrate comprising plasmonic and fluidic features allowed integration of active fluidic elements, such as pneumatic valves, in the top soft thermoplastic cover, increasing device functionality. A simple and compact transmission-based optical setup was employed with multiplexed end-point or dual-channel kinetic detection capability which did not require stringent angular accuracy. The sensitivity, specificity and reproducibility of the transmission SPR biosensor was demonstrated through label-free immunodetection of soluble cell-surface glycoprotein sCD44 at clinically relevant picomolar to nanomolar concentrations.

Arrays of doped and un-doped semiconductors for sensor applications

This numerical investigation proposes to use a lamellar grating of doped semiconductors as the active region of a nanoplasmonic biosensing device. Working with highly doped semiconductors instead of a metal allows controlling the value of the plasma frequency. It is possible to reach a plasma frequency close to the range of detection of the sensor to improve its sensitivity. A red shift of the plasmonic resonance of 10.2 nm for a 10−2 refractive index unit increase can be achieved.

Laser-Generated Au–Ag Nanoparticles For Plasmonic Nucleic Acid Sensing

The development of nanoplasmonic sensing approaches for DNA detection based on the localized plasmonic properties of different metallic NPs fabricated by femtosecond laser ablation with an application for synthetic oligonucleotides as specific probes for genetic sequence variations is presented. The planar surface plasmon resonance (SPR) technique has been used to test oligonucleotide probes specific to rpoB genes of Mycobacterium tuberculosis. Optimal experimental conditions providing efficiency of hybridization between immobilized probe and cDNA target and performance of the SPR method were obtained and applied to the nanoplasmonic biosensing based on colloidal nanoparticles. Gold and silver/gold alloy nanoparticles were fabricated by the “pure” laser ablation method and have shown faster conjugation to thiol-modified DNA and higher stability in hybridization buffer than nanoparticles produced by chemical synthesis. Nanoparticle-enhanced and spectral SPR methods were used to confirm the efficiency of DN...