Portable Surface Plasmon Resonance Research Articles

High-performance portable grating-based surface plasmon resonance sensor using a tunable laser at normal incidence

Surface plasmon resonance (SPR) sensors are among the most sensitive sensors. In such devices, a grating is a compelling alternative to a prism for the excitation of a surface plasmon, especially in the development of sensors for point-of-care applications due to their compactness and cost-effectiveness. Here, we demonstrate the use of a tunable laser in a grating-based SPR system for further miniaturization and integration. The tunable laser working at normal incidence replaces spectral and moving components, while also simplifying the optical setup. Normal incidence is conventionally avoided due to the complexity of the control of degenerated SPR modes. We investigate, both computationally and experimentally, the splitting of the SPR modes at small nonzero incidences, which is lacking in previously reported studies. By optimizing the grating configuration, we were able to diminish the SPR mode splitting phenomenon when the excitation was feasible with the normal incidence configuration. The fabricated sensor showed a high sensitivity of 1101.6 nm/RIU. Notably, the figure of merit of the sensor, defined as the ratio between the sensitivity and bandwidth of the SPR dip, was 229.5. The experimental results were consistent with the simulation results. We also demonstrate its capability for detecting low concentrations of glucose and creatinine with the limit of detection of 14.2 and 19.1 mmol/L, respectively.

A portable surface plasmon resonance (SPR) sensor for the detection of immunoglobulin A in plasma.

A life-threatening anaphylactic shock can occur if a patient with undiagnosed immunoglobulin A (IgA) deficiency (i.e., IgA levels <500 ng/mL) receives IgA-containing blood, hence the need for a rapid, point-of-care (POC) method for IgA deficiency screening. Enzyme-linked immunosorbent assay (ELISA) is routinely used to detect IgA, but this method requires trained specialists and ≥24 h to obtain a result. We developed a surface plasmon resonance (SPR)-based protocol to identify IgA-deficient patients or donors within 1 h. The SPR sensor relies on the detection of IgAs captured by primary antibodies adsorbed on the SPR chip and quantified with secondary antibodies. The sensor was calibrated from 0 to 2000 ng/mL in buffer, IgA-depleted human serum, and plasma samples from IgA-deficient individuals. A critical concentration of 500 ng/mL was set for IgA deficiency. The optimized sensor was then tested on eight plasma samples with known IgA status (determined by ELISA), including five with IgA deficiency and three with normal IgA levels. The limit of detection was estimated at 30 ng/mL in buffer and 400 ng/mL in diluted plasma. The results obtained fully agreed with ELISA among the eight plasma samples tested. The protocol distinguished IgA-deficient from normal samples, even for samples with an IgA concentration closer to critical concentration. In conclusion, we developed a reliable POC assay for the quantification of IgA in plasma. This test may permit POC testing at blood drives and centralized centers to maintain reserves of IgA-deficient blood and in-hospital testing of blood recipients.

A Point-of-Care Testing Device Utilizing Graphene-Enhanced Fiber Optic SPR Sensor for Real-Time Detection of Infectious Pathogens.

Timely detection of highly infectious pathogens is essential for preventing and controlling public health risks. However, most traditional testing instruments require multiple tedious steps and ultimately testing in hospitals and third-party laboratories. The sample transfer process significantly prolongs the time to obtain test results. To tackle this aspect, a portable fiber optic surface plasmon resonance (FO-SPR) device was developed for the real-time detection of infectious pathogens. The portable device innovatively integrated a compact FO-SPR sensing component, a signal acquisition and processing system, and an embedded power supply unit. A gold-plated fiber is used as the FO-SPR sensing probe. Compared with traditional SPR sensing systems, the device is smaller size, lighter weight, and higher convenience. To enhance the detection capacity of pathogens, a monolayer graphene was coated on the sensing region of the FO-SPR sensing probe. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was used to evaluate the performance of the portable device. The device can accurately detect the SARS-CoV-2 spike S1 protein in phosphate-buffered saline (PBS) and artificial saliva within just 20 min, and the device successfully detected cultured SARS-CoV-2 virus. Furthermore, the FO-SPR probe has long-term stability, remaining stable for up to 8 days. It could distinguish between the SARS-CoV-2 spike protein and the MERS-CoV spike protein. Hence, this FO-SPR device provides reliable, rapid, and portable access to test results. It provides a promising point-of-care testing (POCT) tool for on-site screening of infectious pathogens.

Rapid and label-free screening of SARS-CoV-2 virus in the infected human nasopharyngeal swab samples using UiO-66-modified SPR chip

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) virus has become a dangerous human pathogen and caused severe illness that can lead to death. Yet, the standard practical diagnostic tools for detecting the SARS-CoV-2 virus require multi-step assay, including extraction and labeling steps. Thus, a simple and accurate detection tool is incredibly desirable to support on-site screening, preventing its spread. In this work, we developed a portable surface plasmon resonance (SPR) sensor chip modified with metal–organic frameworks (MOF) UiO-66 that serves as an immobilization matrix of single-chain variable fragment (scFv) receptors. Large surface area and good adsorption of UiO-66/scFv-modified surface lead to an improvement of binding capacity towards the protein target of the SARS-CoV-2 receptor binding domain (RBD). We further successfully demonstrated the use of this portable SPR to detect the SARS-CoV-2 virus from patients' nasopharyngeal swab samples. Interestingly, the SPR sensors can directly distinguish the positive and negative patients within 15 minutes on 23 samples, simultaneously, without the need for labeling, and the results are in line with the gold standard PCR tests. In addition, the detection limit of the sensors is 10.085 × 105 virus/mL, which follows the standard of practical screening tools. Therefore, these UiO-66 modified SPR chip sensors offer a rapid, label-free, and low-cost detection of the SARS-CoV-2 virus that can be potentially developed for other infectious diseases.

Advances in Portable Heavy Metal Ion Sensors.

Heavy metal ions, one of the major pollutants in the environment, exhibit non-degradable and bio-chain accumulation characteristics, seriously damage the environment, and threaten human health. Traditional heavy metal ion detection methods often require complex and expensive instruments, professional operation, tedious sample preparation, high requirements for laboratory conditions, and operator professionalism, and they cannot be widely used in the field for real-time and rapid detection. Therefore, developing portable, highly sensitive, selective, and economical sensors is necessary for the detection of toxic metal ions in the field. This paper presents portable sensing based on optical and electrochemical methods for the in situ detection of trace heavy metal ions. Progress in research on portable sensor devices based on fluorescence, colorimetric, portable surface Raman enhancement, plasmon resonance, and various electrical parameter analysis principles is highlighted, and the characteristics of the detection limits, linear detection ranges, and stability of the various sensing methods are analyzed. Accordingly, this review provides a reference for the design of portable heavy metal ion sensing.

Biofilm growth monitoring using guided wave ultralong-range Surface Plasmon Resonance: A proof of concept

Unwelcomed biofilms are problematic in food industries, surgical devices, marine applications, and wastewater treatment plants, essentially everywhere where there is moisture. Very recently, label-free advanced sensors such as localized and extended surface plasmon resonance (SPR) have been explored as tools for monitoring biofilm formation. However, conventional noble metal SPR substrates suffer from low penetration depth (100–300 nm) into the dielectric medium above the surface, preventing the reliable detection of large entities of single or multi-layered cell assemblies like biofilms which can grow up to a few micrometers or more. In this study, we propose using a plasmonic insulator-metal-insulator (IMI) structure (SiO2–Ag–SiO2) with a higher penetration depth based on a diverging beam single wavelength format of Kretschmann configuration in a portable SPR device. An SPR line detection algorithm for locating the reflectance minimum of the device helps to view changes in refractive index and accumulation of the biofilm in real-time down to 10−7 RIU precision. The optimized IMI structure exhibits strong penetration dependence on wavelength and incidence angle. Within the plasmonic resonance, different angles penetrate different depths, showing a maximum near the critical angle. At the wavelength of 635 nm, a high penetration depth of more than 4 μm was obtained. Compared to a thin gold film substrate, for which the penetration depth is only ∼200 nm, the IMI substrate provides more reliable results. The average thickness of the biofilm after 24 h of growth was found to be between 6 and 7 μm with ∼63% live cell volume, as estimated from confocal microscopic images using an image processing tool. To explain this saturation thickness, a graded index biofilm structure is proposed in which the refractive index decreases with the distance from the interface. Furthermore, when plasma-assisted degeneration of biofilms was studied in a semi-real-time format, there was almost no effect on the IMI substrate compared to the gold substrate. The growth rate over the SiO2 surface was higher than on gold, possibly due to differences between surface charge effects. On the gold, the excited plasmon generates an oscillating cloud of electrons, while for the SiO2 case, this does not happen. This methodology can be utilized to detect and characterize biofilms with better signal reliability with respect to concentration and size dependence.

A portable smartphone-based imaging surface plasmon resonance biosensor for allergen detection in plant-based milks

Food allergies are hypersensitivity immune responses triggered by (traces of) allergenic compounds in foods and drinks. The recent trend towards plant-based and lactose-free diets has driven an increased consumption of plant-based milks (PBMs) with the risk of cross-contamination of various allergenic plant-based proteins during the food manufacturing process. Conventional allergen screening is usually performed in the laboratory, but portable biosensors for on-site screening of food allergens at the production site could improve quality control and food safety. Here, we developed a portable smartphone imaging surface plasmon resonance (iSPR) biosensor composed of a 3D-printed microfluidic SPR chip for the detection of total hazelnut protein (THP) in commercial PBMs and compared its instrumentation and analytical performance with a conventional benchtop SPR. The smartphone iSPR shows similar characteristic sensorgrams compared with the benchtop SPR and enables the detection of trace levels of THP in spiked PBMs with the lowest tested concentration of 0.625 μg/mL THP. The smartphone iSPR achieved LoDs of 0.53, 0.16, 0.14, 0.06, and 0.04 μg/mL THP in 10x-diluted soy, oat, rice, coconut, and almond PBMs, respectively, with good correlation with the conventional benchtop SPR system (R2 0.950–0.991). The portability and miniaturized characteristics of the smartphone iSPR biosensor platform make it promising for the future on-site detection of food allergens by food producers.

Multiple protein-patterned surface plasmon resonance biochip for the detection of human immunoglobulin-G.

A portable surface plasmon resonance (SPR) measurement prototype integrated with a multiple protein-patterned SPR biochip is introduced for label-free and selective detection of human immunoglobulin-G (H-IgG). The polyclonal anti-H-IgG antibodies derived from goat, rabbit, and mouse were immobilized through polydimethylsiloxane (PDMS) microchannels to fabricate the patterned SPR biochip. The PDMS surface was functionalized using 3-aminopropyltrimethoxysilane and bonded to carbodiimide-activated gold substrates to construct irreversibly bonded hydrophilic microfluidic chip at room temperature. For SPR measurement, a custom-made system is developed with a high angular scanning accuracy of 0.005° and a wide scanning range of 30°-80° that avoids the conventional requirement of expensive goniometric stages and detector arrays. The SPR biochip immobilized with 750μg/mL goat anti-H-IgG demonstrated detection of H-IgG with a detection limits of 15 μg/mL, and linear response through a wide concentration range (15-225 μg/mL) of high coefficient of determination (R2 =0.99661). The selectivity of the sensor was investigated by exposing them to two different non-specific targets (bovine serum albumin and polyvalent antivenom). The results indicate negligible sensor response towards nonspecific targets (0.25° for 30 μg/mL bovine serum albumin (BSA) and 0.25° for 30 μg/mL polyvalent antivenom) in comparison to H-IgG (1.5° for 30 μg/mL).

A Near-Infrared Plasmonic Sensor Based on Wedge Fiber-Optic for Ultra-Sensitive Hg Detection

The growing number of serious diseases caused by ever-increasing heavy metal ions pollution have necessitated the use of ion sensors in healthcare and environment monitoring systems. Even with low concentrations heavy metal ions can cause significant harm, so ultra-sensitive on-site and label-free monitoring of heavy metal ions is of great importance. In this work, a simple, portable and high sensitivity optical fiber surface plasmon resonance (SPR) sensor is demonstrated for the detection of Hg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> . On the basis of the investigation of the effects of different incident angles, the optical fiber sensor adopts wedged tip probe with a 75° incident angle. The plasmonic sensor exhibits a superior refractive index bulk sensitivity of up to 13830 nm/RIU in near-infrared band, which is a further step in ultrasensitive sensing detection, compared with the traditional optical fiber SPR sensors. In addition, we validate the optical fiber sensor's performance for Hg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> sensing. By self-assembling monolayer of 1,6-Hexanedithiol (HDT) on the sensing surface, the Au-coated fiber-optic probe is modified to capture Hg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> . The lowest detection limit is found to be 0.324 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf{ug}/\mathbf{mL}$</tex-math></inline-formula> for the near-infrared band and the sensitivity can reach up to 0.22 nm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$({\mathbf{ug}/\mathbf{mL}})$</tex-math></inline-formula> . The experimental results show the excellent promise for our sensor in applications of environmental monitoring due to high sensitivity, selectivity and low-cost.

Synthesis of Molecularly Imprinted Polymer Nanoparticles for SARS-CoV-2 Virus Detection Using Surface Plasmon Resonance

COVID-19 caused by a SARS-CoV-2 infection was first reported from Wuhan, China, and later recognized as a pandemic on March 11, 2020, by the World Health Organization (WHO). Gold standard nucleic acid and molecular-based testing have largely satisfied the requirements of early diagnosis and management of this infectious disease; however, these techniques are expensive and not readily available for point-of-care (POC) applications. The COVID-19 pandemic of the 21st century has emphasized that medicine is in dire need of advanced, rapid, and cheap diagnostic tools. Herein, we report on molecularly imprinted polymer nanoparticles (MIP-NPs/nanoMIPs) as plastic antibodies for the specific detection of SARS-CoV-2 by employing a surface plasmon resonance (SPR) sensor. High-affinity MIP-NPs directed against SARS-CoV-2 were manufactured using a solid-phase imprinting method. The MIP-NPs were then characterized using dynamic light scattering (DLS) and atomic force microscopy (AFM) prior to their incorporation into a label-free portable SPR device. Detection of SARS-CoV-2 was studied within a range of 104–106 PFU mL−1. The MIP-NPs demonstrated good binding affinity (KD = 0.12 pM) and selectivity toward SARS-CoV-2. The AFM, cyclic voltammetry, and square-wave voltammetry studies revealed the successful stepwise preparation of the sensor. A cross-reactivity test confirmed the specificity of the sensor. For the first time, this study demonstrates the potential of molecular imprinting technology in conjunction with miniaturized SPR devices for the detection of SARS-CoV-2 particles with high-affinity and specificity. Such sensors could help monitor and manage the risks related to virus contamination and infections also beyond the current pandemic.

Development of COVID-19 Detection Using SPR Sensors: A Preliminary Result

Coronavirus disease or COVID-19 is a virus from the Coronaviridae family that has caused pandemics throughout the world since the end of 2019. The virus spreads ten times faster through human interaction than SARS-CoV. The RNA sequence of COVID-19 has a 79.5% similarity with SARS-CoV. Fast and specific detection of COVID-19 is needed so that patient detection can be done quickly and accurately. One method that can be developed as a COVID-19 biosensor is aptamers-based biosensors. The aptamer is an artificial oligo nucleic acid that can specifically bind to target molecules. The aptamer is easily and chemically modifiable for increasing stability and reducing toxicity. It shows a comparable affinity for the target virus and better thermal stability than monoclonal antibodies. This advantage makes aptamer a promising candidate in diagnostic and detection applications. The goal of this research is to use an RNA aptamer as the specific recognition element in a portable surface plasmon resonance (SPR) biosensor for the detection of COVID-19 in humans. An aptamer RNA 1 COVID-19 was designed using the COVID-19 sequence from GISAID using the in silico method. End of 3’ aptamer RNA 1 was modified with dithiol. And Then, the aptamer was immobilized on the gold nanoparticle sensor surface via Cysteine-dithiol binding. The RNA solution, that had been extracted from swab samples, was diluted ten times before being used as a sample. The immobilized aptamer RNA 1 captured COVID-19 in RNA solution, causing an increase in refraction index (r.u). An aptamer RNA 1 was found to bind RNA virus of COVID-19 where the positive sample of COVID-19 has refraction index (r.u) between 3 r.u – 10 r.u for various Ct values.

Rapid Determination of Methamphetamine and Cocaine in Saliva by Portable Surface Plasmon Resonance (SPR)

Methamphetamine (MA) and cocaine (COC) are among the most abused drugs worldwide. In this study, a portable dual-channel surface plasmon resonance (SPR) biosensor based on an indirect inhibitive immunoassay was developed for the rapid and simultaneous determination of MA and COC in saliva. MA-bovine serum albumin (MA-BSA) and COC-BSA conjugates were prepared as antigens and immobilized on the sensor chip in each channel. Upon contact with the surface-immobilized antigens, MA monoclonal antibody (MA-Ab) or COC monoclonal antibody (COC-Ab) enhanced the SPR signal. The bonding of the antibodies to antigens was inhibited by the presence of MA or COC in the samples. The concentrations of the antigens and antibodies were optimized, and the resulting SPR inhibitive immunoassay exhibited good sensitivity, with limits of detection for MA and COC equal to 0.95 and 3.14 ng·mL−1, respectively. These values are below the legal limits of these drugs for vehicle drivers in China. Furthermore, the suitability of the method was confirmed using saliva from healthy donors, which demonstrated acceptable specificities with satisfactory recoveries. The results indicate that the portable SPR biosensor is facile and rapid for the sensitive determination of abused drugs.

Analysis of protein-heparin interactions using a portable SPR instrument

Optical biosensors such as those based on surface plasmon resonance (SPR) are a key analytical tool for understanding biomolecular interactions and function as well as the quantitative analysis of analytes in a wide variety of settings. The advent of portable SPR instruments enables analyses in the field. A critical step in method development is the passivation and functionalisation of the sensor surface. We describe the assembly of a surface of thiolated oleyl ethylene glycol/biotin oleyl ethylene glycol and its functionalisation with streptavidin and reducing end biotinylated heparin for a portable SPR instrument. Such surfaces can be batch prepared and stored. Two examples of the analysis of heparin-binding proteins are presented. The binding of fibroblast growth factor 2 and competition for the binding of a heparan sulfate sulfotransferase by a library of selectively modified heparins and suramin, which identify the selectivity of the enzyme for sulfated structures in the polysaccharide and demonstrate suramin as a competitor for the enzyme’s sugar acceptor site. Heparin functionalised surfaces should have a wide applicability, since this polysaccharide is a close structural analogue of the host cell surface polysaccharide, heparan sulfate, a receptor for many endogenous proteins and viruses.

Sensing of COVID-19 spike protein in nasopharyngeal samples using a portable surface plasmon resonance diagnostic system

Rapid, yet sensitive and accurate testing concepts are critical in the control of spreading viral diseases.

Portable fiber-optic SPR platform for the detection of NS1-antigen for dengue diagnosis

Here, we present a portable, selective and cost-effective fiber-optic surface plasmon resonance (SPR) based platform for early detection of Dengue virus. NS1 protein was targeted as the biomarker of dengue. Antibody-antigen specific binding was exploited for NS1 antigen detection. The binding of antibody was assisted by a self-assembled monolayer of alkanethiols on the surface of silver-coated unclad fiber. A wavelength interrogation mode of SPR was utilized to detect NS1 antigen in the dynamic range of 0.2–2.0 μg/ml. The 40 nm thick silver coated optical fiber exhibited resonance wavelength around 500 nm and change in resonance wavelength was monitored for each attachment step on the fiber. The sensitivity at the lowest concentration of NS1 antigen was found to be 54.7 nm/(μg/ml). The limit of detection of the sensor was found to be 0.06 μg/ml, which lies in the physiological range of NS1 protein present in the infected blood, hence the present technique may provide a very early detection advantage. Real blood serum samples were also successfully tested on the set-up, confirming compatibility with the conventional methods. The presented field-deployable platform has wide applications in mass monitoring of dengue, such as during outbreaks and epidemics.

A portable optical fiber biosensor for the detection of zearalenone based on the localized surface plasmon resonance

Abstract With the continuous improvement of people's living standards, food safety issues have gradually become one of the main concerns. Rapid and accurate detection of zearalenone (ZEN) in food has attracted broad research interest. In this work, a low-cost, portable, and reusable optical fiber-based localized surface plasmon resonance (LSPR) biosensor for ZEN was developed. Gold nanoparticles around 25 nm were synthesized and coated on the cross-section of the end of an optical fiber, and then the ZEN nucleic acid aptamer was modified to form the LSPR biosensor for ZEN detection. Results showed that there was a good relationship between ZEN concentrations and the redshifts of LSPR peak in the range of 1 ∼ 480 ng/mL, the limit of detection was 0.102 ng/mL. Moreover, the sensing interface could be easily regenerated by cutting and polishing the end of the optical fiber, indicating that the LSPR biosensor was reusable. It also has exceptional high selectivity for ZEN and good recovery and repeatability, which has a good prospect for the on-site ZEN monitoring.

MobileSPR App and Case: A Combined Logical and Mechanical Solution for Surface Plasmon Resonance Sensors Based on Smartphone

This paper proposes a mechanical structure (MobileSPR Case) combined with mobile application (MobileSPR App) to provide a complete solution for surface plasmon resonance (SPR) sensor based on smartphones. The mechanical structure was specially designed to hold all optical elements on the smartphone to archive the surface plasmon excitation. Manufactured in a 3D printer, the case fit from the top, and is adjustable for several frontal camera dispositions. Composed of two parts, makes the smartphone replacement process easier, as well enable thin- and thicker- biochips for surface plasmon excitation. The embedded application controls light source, camera, data process, information displayed and results storage, avoid an extra components to create a portable SPR solution. The App manipulate the light beams provided by the smartphone screen, varying the color between 380 nm to 780 nm, allowing the usage with biochips of different materials, metal layer and configurations. To demonstrates the solution feasibility a Xiaomi MI 9 Lite smartphone was used. Both a flat (thin) and trapezoidal (thicker) biochips operating in the angular interrogation were attached in the MobileSPR Case & App solution, and aqueous substances were exploited experimentally.

Cross-validation of ELISA and a portable surface plasmon resonance instrument for IgG antibody serology with SARS-CoV-2 positive individuals.

We report on the development of surface plasmon resonance (SPR) sensors and matching ELISAs for the detection of nucleocapsid and spike antibodies specific against the novel coronavirus 2019 (SARS-CoV-2) in human serum, plasma and dried blood spots (DBS). When exposed to SARS-CoV-2 or a vaccine against SARS-CoV-2, the immune system responds by expressing antibodies at levels that can be detected and monitored to identify the fraction of the population potentially immunized against SARS-CoV-2 and support efforts to deploy a vaccine strategically. A SPR sensor coated with a peptide monolayer and functionalized with various sources of SARS-CoV-2 recombinant proteins expressed in different cell lines detected human anti-SARS-CoV-2 IgG antibodies in clinical samples. Nucleocapsid expressed in different cell lines did not significantly change the sensitivity of the assays, whereas the use of a CHO cell line to express spike ectodomain led to excellent performance. This bioassay was performed on a portable SPR instrument capable of measuring 4 biological samples within 30 minutes of sample/sensor contact and the chip could be regenerated at least 9 times. Multi-site validation was then performed with in-house and commercial ELISA, which revealed excellent cross-correlations with Pearson's coefficients exceeding 0.85 in all cases, for measurements in DBS and plasma. This strategy paves the way to point-of-care and rapid testing for antibodies in the context of viral infection and vaccine efficacy monitoring.

Gold nanoparticle-assisted plasmonic enhancement for DNA detection on a graphene-based portable surface plasmon resonance sensor

The impact of different gold nanoparticle (GNP) structures on plasmonic enhancement for DNA detection is investigated on a few-layer graphene (FLG) surface plasmon resonance (SPR) sensor. Two distinct structures of gold nano-urchins (GNu) and gold nanorods (GNr) were used to bind the uniquely designed single-stranded probe DNA (ssDNA) of Mycobacterium tuberculosis complex DNA. The two types of GNP-ssDNA mixture were adsorbed onto the FLG-coated SPR sensor through the π-π stacking force between the ssDNA and the graphene layer. In the presence of complementary single-stranded DNA, the hybridization process took place and gradually removed the probes from the graphene surface. From SPR sensor preparation, the annealing process of the Au layer of the SPR sensor effectively enhanced the FLG coverage leading to a higher load of the probe DNA onto the sensing interface. The FLG was shown to be effective in providing a larger surface area for biomolecular capture due to its roughness. Carried out in the DNA hybridization study with the SPR sensor, GNu, with its rough and spiky structures, significantly reinforced the overall DNA hybridization signal compared with GNr with smooth superficies, especially in capturing the probe DNA. The DNA hybridization detection assisted by GNu reached the femtomolar range limit of detection. An optical simulation validated the extreme plasmonic field enhancement at the tip of the GNu spicules. The overall integrated approach of the graphene-based SPR sensor and GNu-assisted DNA detection provided the proof-of-concept for the possibility of tuberculosis disease screening using a low-cost and portable system to be potentially applied in remote or third-world countries.

Development of a Portable SPR Sensor for Nucleic Acid Detection.

Nucleic acid detection is of great significance in clinical diagnosis, environmental monitoring and food safety. Compared with the traditional nucleic acid amplification detection method, surface plasmon resonance (SPR) sensing technology has the advantages of being label-free, having simple operation, and providing real-time detection. However, the angle scanning system in many SPR angle modulation detection applications usually requires a high-resolution stepper motor and complex mechanical structure to adjust the angle. In this paper, a portable multi-angle scanning SPR sensor was designed. The sensor only uses one stepping motor to rotate a belt, and the belt pulls the mechanical linkages of incident light and reflected light to move in opposite directions for achieving the SPR angle scanning mode that keeps the incident angle and reflected angle equal. The sensor has an angle scanning accuracy of 0.002°, response sensitivity of 3.72 × 10−6 RIU (refractive index unit), and an angle scanning range of 30°–74°. The overall size of the system is only 480 mm × 150 mm × 180 mm. The portable SPR sensor was used to detect nucleic acid hybridization on a gold film chip modified with bovine serum albumin (BSA). The result revealed that the sensor had high sensitivity and fast response, and could successfully accomplish the hybridization detection of target DNA solution of 0.01 μmol/mL.