HER2 biosensing through SPR-envelope tracking in plasmonic optical fiber gratings

All-fiber label-free optical fiber biosensors: from modern technologies to current applications [Invited]

Biosensors are established as promising analytical tools for detecting various analytes important in biomedicine and environmental monitoring. Using fiber optic technology as a sensing element in biosensors offers low cost, high sensitivity, chemical inertness, and immunity to electromagnetic interference. Optical fiber sensors can be used in in vivo applications and multiplexed to detect several targets simultaneously. Certain configurations of optical fiber technology allow the detection of analytes in a label-free manner. This review aims to discuss recent advances in label-free optical fiber biosensors from a technological and application standpoint. First, modern technologies used to build label-free optical fiber-based sensors will be discussed. Then, current applications where these technologies are applied are elucidated. Namely, examples of detecting soluble cancer biomarkers, hormones, viruses, bacteria, and cells are presented.

A D-Shaped Polymer Optical Fiber Surface Plasmon Resonance Biosensor for Breast Cancer Detection Applications

Fiber-optic biosensors have garnered significant attention and witnessed rapid development in recent years owing to their remarkable attributes such as high sensitivity, immunity to electromagnetic interference, and real-time monitoring. They have emerged as a potential tool in the realm of biomarker detection for low-concentration and small molecules. In this paper, a portable and cost-effective optical fiber biosensor based on surface plasmon resonance for the early detection of breast cancer is demonstrated. By utilizing the aptamer human epidermal growth factor receptor 2 (HER2) as a specific biomarker for breast cancer, the presence of the HER2 protein can be detected through an antigen-antibody binding technique. The detection method was accomplished by modifying a layer of HER2 aptamer on the flat surface of a gold-coated D-shaped polymer optical fiber (core/cladding diameter 120/490 μm), of which the residual thickness after side-polishing was about 245 μm, the thickness of the coated gold layer was 50 nm, and the initial wavelength in pure water was around 1200 nm. For low-concentration detection of the HER2 protein, the device exhibited a wavelength shift of ~1.37 nm with a concentration of 1 μg/mL (e.g., 5.5 nM), which corresponded to a limit of detection of ~5.28 nM. Notably, the response time of the biosensor was measured to be as fast as 5 s. The proposed biosensor exhibits the potential for early detection of HER2 protein in initial cancer serum and offers a pathway to early prevention of breast cancer.

Plasmonic biosensing with tilted fiber Bragg gratings interrogated using a 512-pixel spectrometer

Plasmonic tilted fiber Bragg gratings (TFBGs) are very efficient for fast, accurate, and minimally invasive biosensing. Their transmitted amplitude spectrum is a dense comb of narrowband cladding mode resonances (full width at half maximum < 1 nm) that is usually demodulated using highly resolved (wavelength resolution < 10 pm) devices. This work demonstrates the possibility of using a coarsely resolved spectrometer (166 pm) to read out the amplitude spectrum of a gold-coated TFBG. A refined analysis of the spectral content has allowed us to develop signal processing that provides a refractometric sensitivity of 2656 nm/RIU. This is a fivefold improvement compared to previously reported read-out techniques. Biosensing has then been successfully implemented with gold-coated TFBGs implemented in reflection mode for the detection of insulin, with specific antibodies grafted on the gold surface. Our experimental work is a first step toward the industrialization of the FBG technology, as it opens the door to fast parallel biosensing, profiting from the multiple sensing channels (up to 64) of the interrogator and its high processing speed (repetition rate up to 3 kHz).

Wave-theory-based analysis of a fiber optic bio-sensor illuminated by radially polarized Bessel-Gauss beam: an approach for early diagnosis of breast cancer with a high-resolution wavelength-interrogation technique

With the establishment of validity using authoritative experimental results, an analytical investigation of an SPR-based fiber optic sensor, employing a wave-theory-based technique for determining breast cancer by shining a radially polarized Bessel-Gauss (RPBG) beam, is proposed. First, by using a radially polarized Gaussian (RPG) beam, the observed sensitivity is 9404.61 dB/RIU, where the acquired results are in good concurrence with the experimental data reported by Yan et al. [Chin. Opt. Lett.7, 909 (2009)COLHBT1671-7694]. Thus, the proposed theory has been validated with the reported experimental data. This theoretical analysis is further extended by utilizing an RPBG beam, where the observed sensitivity is 21,699.26 dB/RIU and 5846 nm/RIU, with a resolution of 4.61×10^-7, which is 2.5 times superior to the reported results to date. By using an RPBG beam, the proposed method, to our best knowledge, is the first to achieve much higher sensitivity in the area of fiber optic breast cancer detection. The higher sensitivity achieved at lower concentrations of an HER2 biomarker has led to the idea of early diagnosis of breast cancer by optically assessing it at its earlier stage using a high-resolution wavelength-interrogation technique.

Optical biosensor based on weak value amplification for the high sensitivity detection of Pertuzumab in combination with Trastuzumab binding to the extracellular domain of HER2

A real-time optical phase sensing scheme based on weak value amplification was proposed to monitor the especially binding process of Pertuzumab combined with Trastuzumab on HER2 positive cells. From the wavelength shift of output spectrum, the phase difference between measuring and referential path related to the concentration of Pertuzumab as well as Trastuzumab could be calculated. With this approach, the limit of detection (LOD) of 5.54 × 10^-13 M for Pertuzumab assay was achieved. Besides, the kinetics signal of Pertuzumab in combination with Trastuzumab binding to HER2 was detected in real time. Experimental results demonstrated that both Trastuzumab and Pertuzumab can be captured by HER2, but the former was significantly superior to the latter in terms of the target number. Additionally, the binding speed was analyzed and demonstrated to be closely correlated with the initial concentration of the targeting agents.

Ultralow Limit Detection of Soluble HER2 Biomarker in Serum with a Fiber-Optic Ball-Tip Resonator Assisted by a Tilted FBG

An optical-fiber biosensor has been developed for the detection of the breast cancer biomarker soluble human epidermal growth factor receptor-2 (sHER2). The sensor was fabricated by combining a tilted fiber Bragg grating (TFBG) with a ball resonator, allowing us to achieve an excellent sensitivity compared to other optical-fiber-based sensors. The sensor exhibits a resonance comb excited by the TFBG and the spectral profile of the ball resonator. The detection of sHER2 at extremely low concentrations was carried out by tracking the amplitude change of selected resonances. The therapeutic anti-HER2 monoclonal antibody Trastuzumab has been used to functionalize the biosensor with silane surface chemistry. The sensor features a sensitivity of 4034 dB/RIU with a limit of detection (LoD) in buffer and in a 1/10 diluted serum of 151.5 ag/mL and 3.7 pg/mL, respectively. At relatively high protein concentrations (64 ng/mL) binding to sHER (7.36 dB) as compared to control proteins (below 0.7 dB) attested the high specificity of sHER2 detection.

Plasmonics-based gas sensor with photonic spin hall effect in broad terahertz frequency range under variable chemical potential of graphene

Graphene monolayer of sub-nanometer thickness possesses strong metallic and plasmonic behavior in a broad terahertz (THz) frequency range. This plasmonic effect can be considerably manipulated when graphene layer is subjected to a variable chemical potential (E_f) via chemical doping or electrical gating. The strong adsorption characteristics of graphene layer is another important advantage. In this work, a photonic spin Hall effect (PSHE) based plasmonic sensor consisting of germanium prism, organic dielectric layer, and graphene monolayer is simulated and analyzed in THz range aiming at highly sensitive and reliable gas sensing. Modified Otto configuration and Kubo formulation for graphene at room temperature are considered. The sensor's performance is examined in terms of figure of merit (FOM). The analysis indicates that under angular interrogation scheme of sensor operation, the FOM improves for smaller chemical potential (moderate doping) and higher THz frequency. Moreover, the influence of temperature on gas sensor's performance (FOM) is negligible, which suggests that the sensor is capable of providing stable sensing performance against temperature variation. The sensor design is highly flexible in terms of selection of THz frequency as an alternative interrogation scheme (i.e., measuring the variation in spin-dependent shift peak value of PSHE spectrum upon change in gas medium refractive index) can also be implemented. It is found that there is no need to change the moderate doping of graphene monolayer (i.e., E_f remains around its normal value ~ 0.1 eV) as the sensitivity achievable with this alternative method has considerably greater magnitude at smaller THz frequency (e.g., 2 THz). The magnitudes of FOM (with angular interrogation method) and sensitivity (with alternative method) are found to be significantly greater for rarer gaseous media, which might possibly assist in early detection of airborne viruses such as SARS-Cov-2 (while using appropriate specificity method) and to measure the concentration of a particular gas in a given gaseous mixture.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11082-022-03626-7.

Cladding Mode Fitting-Assisted Automatic Refractive Index Demodulation Optical Fiber Sensor Probe Based on Tilted Fiber Bragg Grating and SPR

In the paper based on surface plasmon resonance (SPR) in a tilted fiber Bragg grating (TFBG), a novel algorithm is proposed, which facilitates demodulation of surrounding refractive index (SRI) via cladding mode interrogation and accelerates calibration and measurement of SRI. Refractive indices with a tiny index step of 2.2 × 10⁻⁵ are prepared by the dilution of glucose aqueous solution for the test and the calibration of this fiber sensor probe. To accelerate the calibration process, automatic selection of the most sensitive cladding mode is demonstrated. First, peaks of transmitted spectrum are identified and numbered. Then, sensitivities of several potentially sensitive cladding modes in amplitude adjacent to the left of the SPR area are calculated and compared. After that, we focus on the amplitudes of the cladding modes as a function of a SRI, and the highest sensitivity of −6887 dB/RIU (refractive index unit) is obtained with a scanning time of 15.77 s in the range from 1520 nm to 1620 nm. To accelerate the scanning speed of the optical spectrum analyzer (OSA), the wavelength resolution is reduced from 0.028 nm to 0.07 nm, 0.14 nm, and 0.28 nm, and consequently the scanning time is shortened to 6.31 s, 3.15 s, and 1.58 s, respectively. However, compared to 0.028 nm, the SRI sensitivity for 0.07 nm, 0.14 nm, and 0.28 nm is reduced to −5685 dB/RIU (17.5% less), −5415 dB/RIU (21.4% less), and −4359 dB/RIU (36.7% less), respectively. Thanks to the calculation of parabolic equation and weighted Gauss fitting based on the original data, the sensitivity is improved to −6332 dB/RIU and −6721 dB/RIU, respectively, for 0.07 nm, and the sensitivity is increased to −5850 dB/RIU and −6228 dB/RIU, respectively, for 0.14 nm.

Recent advances in biosensor devices for HER-2 cancer biomarker detection

The human epidermal growth factor receptor 2 (HER-2) protein is a member of the epidermal growth factor receptor (EGFR or ErbB) family and is a transmembrane tyrosine kinase receptor. HER-2 is highly regulated in ovarian, lung, gastric, oral, and breast cancers. The low specificity, complexity, expensiveness and the lack of sensitivity are essential restrictions in traditional diagnosis methods such as FISH, immunohistochemistry and PCR and these disadvantages led to the need for more studies on alternative methods. Biosensor technology has greatly affected the quality of human life owing to its features including, sensitivity, specificity, and rapid diagnosis and monitoring of different patient diseases. In this review article, we examine various biosensors, considering that they have been categorized based on the transducers used including piezoelectric biosensors, optical sensors such as fluorescence and surface plasmon resonance, and electrochemical types for the diagnosis of HER-2 and the effectiveness of some drugs against that. Attention to developing some types of biosensor devices such as colorimetric biosensors for HER-2 detection can be an important point in future studies.

Optimization of Cladding Diameter for Refractive Index Sensing in Tilted Fiber Bragg Gratings

This work presents an experimental investigation of the effect of chemical etching on the refractive index (RI) sensitivity of tilted fiber Bragg gratings (TFBGs). Hydrofluoric acid (HF) was used stepwise in order to reduce the optical fiber diameter from 125 µm to 13 µm. After each etching step, TFBGs were calibrated using two ranges of RI solutions: the first one with high RI variation (from 1.33679 RIU to 1.37078 RIU) and the second with low RI variation (from 1.34722 RIU to 1.34873 RIU). RI sensitivity was analyzed in terms of wavelength shift and intensity change of the grating resonances. The highest amplitude sensitivities obtained are 1008 dB/RIU for the high RI range and 8160 dB/RIU for the low RI range, corresponding to the unetched TFBG. The highest wavelength sensitivities are 38.8 nm/RIU for a fiber diameter of 100 µm for the high RI range, and 156 nm/RIU for a diameter of 40 µm for the small RI range. In addition, the effect of the etching process on the spectral intensity of the cladding modes, their wavelength separation and sensor linearity (R²) were studied as well. As a result, an optimization of the etching process is provided, so that the best trade-off between sensitivity, intensity level, and fiber thickness can be obtained.

Relevance of the Spectral Analysis Method of Tilted Fiber Bragg Grating-Based Biosensors: A Case-Study for Heart Failure Monitoring

Optical fiber technology has rapidly progressed over the years, providing valuable benefits for biosensing purposes such as sensor miniaturization and the possibility for remote and real-time monitoring. In particular, tilted fiber Bragg gratings (TFBGs) are extremely sensitive to refractive index variations taking place on their surface. The present work comprises a case-study on the impact of different methods of analysis applied to decode spectral variations of bare and plasmonic TFBGs during the detection of N-terminal B-type natriuretic peptide (NT-proBNP), a heart failure biomarker, namely by following the most sensitive mode, peaks of the spectral envelopes, and the envelopes’ crossing point and area. Tracking the lower envelope resulted in the lowest limits of detection (LOD) for bare and plasmonic TFBGs, namely, 0.75 ng/mL and 0.19 ng/mL, respectively. This work demonstrates the importance of the analysis method on the outcome results, which is crucial to attain the most reliable and sensitive method with lower LOD sensors. Furthermore, it makes the scientific community aware to take careful attention when comparing the performance of different biosensors in which different analysis methods were used.

Recent advances in the selection of cancer-specific aptamers for the development of biosensors

An early diagnosis has the potential to greatly decrease cancer mortality. For that purpose, specific cancer biomarkers have been molecularly targeted by aptamer sequences to enable an accurate and rapid detection. Aptamer-based biosensors for cancer diagnostics are a promising alternative to those using antibodies, due to their high affinity and specificity to the target molecules and advantageous production. Synthetic nucleic acid aptamers are generated by in vitro Systematic Evolution of Ligands by Exponential enrichment (SELEX) methodologies that have been improved over the years to enhance the efficacy and to shorten the selection process. Aptamers have been successfully applied in electrochemical, optical, photoelectrochemical and piezoelectrical-based detection strategies. These aptasensors comprise a sensitive, accurate and inexpensive option for cancer detection being used as point-of-care devices. This review highlights the recent advances in cancer biomarkers, achievements and optimizations made in aptamer selection, as well as the different aptasensors developed for the detection of several cancer biomarkers.

In-Situ Li-Ion Pouch Cell Diagnostics Utilising Plasmonic Based Optical Fibre Sensors

As the drive to improve the cost, performance characteristics and safety of lithium-ion batteries increases with adoption, one area where significant value could be added is that of battery diagnostics. This paper documents an investigation into the use of plasmonic-based optical fibre sensors, inserted internally into 1.4 Ah lithium-ion pouch cells, as a real time and in-situ diagnostic technique. The successful implementation of the fibres inside pouch cells is detailed and promising correlation with battery state is reported, while having negligible impact on cell performance in terms of capacity and columbic efficiency. The testing carried out includes standard cycling and galvanostatic intermittent titration technique (GITT) tests, and the use of a reference electrode to correlate with the anode and cathode readings separately. Further observations are made around the sensor and analyte interaction mechanisms, robustness of sensors and suggested further developments. These finding show that a plasmonic-based optical fibre sensor may have potential as an opto-electrochemical diagnostic technique for lithium-ion batteries, offering an unprecedented view into internal cell phenomena.

Overview and emerging trends in optical fiber aptasensing

Optical fiber biosensors have attracted growing interest over the last decade and quickly became a key enabling technology, especially for the detection of biomarkers at extremely low concentrations and in small volumes. Among the many and recent fiber-optic sensing amenities, aptamers-based sensors have shown unequalled performances in terms of ease of production, specificity, and sensitivity. The immobilization of small and highly stable bioreceptors such as DNA has bolstered their use for the most varied applications e.g., medical diagnosis, food safety and environmental monitoring. This review highlights the recent advances in aptamer-based optical fiber biosensors. An in-depth analysis of the literature summarizes different fiber-optic structures and biochemical strategies for molecular detection and immobilization of receptors over diverse surfaces. In this review, we analyze the features offered by those sensors and discuss about the next challenges to be addressed. This overview investigates both biochemical and optical parameters, drawing the guiding lines for forthcoming innovations and prospects in this ever-growing field of research.

PfHRP2 detection using plasmonic optrodes: performance analysis

Background

Early malaria diagnosis and its profiling require the development of new sensing platforms enabling rapid and early analysis of parasites in blood or saliva, aside the widespread rapid diagnostic tests (RDTs).

Methods

This study shows the performance of a cost-effective optical fiber-based solution to target the presence of Plasmodium falciparum histidine-rich protein 2 (PfHRP2). Unclad multimode optical fiber probes are coated with a thin gold film to excite Surface Plasmon Resonance (SPR) yielding high sensitivity to bio-interactions between targets and bioreceptors grafted on the metal surface.

Results

Their performances are presented in laboratory conditions using PBS spiked with growing concentrations of purified target proteins and within in vitro cultures. Two probe configurations are studied through label-free detection and amplification using secondary antibodies to show the possibility to lower the intrisic limit of detection.

Conclusions

As malaria hits millions of people worldwide, the improvement and multiplexing of this optical fiber technique can be of great interest, especially for a future purpose of using multiple receptors on the fiber surface or several coated-nanoparticles as amplifiers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-021-03863-3.

Plasmonic sensors based on tilted Bragg gratings in multicore optical fibers

Bare and gold-coated tilted fiber Bragg gratings (TFBGs) can nowadays be considered as a mature technology for volume and surface refractometric sensing, respectively. As for other technologies, a continuous effort is made towards the production of even more sensitive sensors, thereby enabling a high-resolution screening of the surroundings and the possible detection of rare events. To this aim, we study in this work the development of TFBG refractometers in 4-core fibers. In particular, we show that the refractometric sensitivity of the cut-off mode can reach 100 nm/RIU for a bare grating. Using another demodulation method, a tenfold sensitivity increase is obtained when tracking the extremum of the SPR (surface plasmon resonance) envelope for a gold-coated TFBG configuration. Immobilization of DNA probes was performed as a proof-of-concept to assess the high surface sensitivity of the device.

Hybrid LPG-FBG Based High-Resolution Micro Bending Strain Sensor

Sensitivity and reliability are essential factors for the practical implementation of a wearable sensor. This study explores the possibility of using a hybrid high-resolution Bragg grating sensor for achieving a fast response to dynamic, continuous motion and Bragg signal pattern monitoring measurement. The wavelength shift pattern for real-time monitoring in picometer units was derived by using femtosecond laser Bragg grating processing on an optical wave path with long-period grating. The possibility of measuring the demodulation system's Bragg signal pattern on the reflection spectrum of the femtosecond laser precision Bragg process and the long-period grating was confirmed. By demonstrating a practical method of wearing the sensor, the application of wearables was also explored. It is possible to present the applicability of sophisticated micro transformation measurement applications in picometer units.

Detection of Bacterial and Viral Pathogens Using Photonic Point-of-Care Devices

Infectious diseases caused by bacteria and viruses are highly contagious and can easily be transmitted via air, water, body fluids, etc. Throughout human civilization, there have been several pandemic outbreaks, such as the Plague, Spanish Flu, Swine-Flu, and, recently, COVID-19, amongst many others. Early diagnosis not only increases the chance of quick recovery but also helps prevent the spread of infections. Conventional diagnostic techniques can provide reliable results but have several drawbacks, including costly devices, lengthy wait time, and requirement of trained professionals to operate the devices, making them inaccessible in low-resource settings. Thus, a significant effort has been directed towards point-of-care (POC) devices that enable rapid diagnosis of bacterial and viral infections. A majority of the POC devices are based on plasmonics and/or microfluidics-based platforms integrated with mobile readers and imaging systems. These techniques have been shown to provide rapid, sensitive detection of pathogens. The advantages of POC devices include low-cost, rapid results, and portability, which enables on-site testing anywhere across the globe. Here we aim to review the recent advances in novel POC technologies in detecting bacteria and viruses that led to a breakthrough in the modern healthcare industry.