Hybridized nanolayer modified Ω-shaped fiber-optic synergistically enhances localized surface plasma resonance for ultrasensitive cytosensor and efficient photothermal therapy

A disposable fiber-optic plasmonic sensor for chemical sensing

The integration of fiber optics and plasmonic sensors is promising to improve the practical usability over conventional bulky sensors and systems. To achieve high sensitivity, it typically requires fabrication of well-defined plasmonic nanostructures on optical fibers, which greatly increases the cost and complexity of the sensors. Here, we present a fiber-optic sensor system by using chemical absorption of gold nanoparticles and a replaceable configuration. By functioning gold nanoparticles with aptamers or antibodies, we demonstrate the applications in chemical sensing using two different modes. Measuring shift in resonance wavelength enables the Pb2+ detection with a high linearity and a limit of detection of 0.097 nM, and measuring absorption peak amplitude enables the detection of E. coli in urinary tract infection with a dynamic range between 103 to 108 CFU/mL. The high sensitivity, simple fabrication and disposability of this sensing approach could pave the way for point-of-care testing with fiber-optic plasmonic sensors.

Simultaneous noninvasive ultrasensitive detection of prostate specific antigen and lncRNA PCA3 using multiplexed dual optical microfibers with strong plasmonic nanointerfaces

Low accuracy of diagnosing prostate cancer (PCa) was easily caused by only assaying single prostate specific antigen (PSA) biomarker. Although conventional reported methods for simultaneous detection of two specific PCa biomarkers could improve the diagnostic efficiency and accuracy, low detection sensitivity restrained their use in extreme early-stage PCa clinical assay applications. In order to overcome above drawbacks, this paper herein proposed a multiplexed dual optical microfibers separately functionalized with gold nanorods (GNRs) and Au nanobipyramids (Au NBPs) nanointerfaces with strong localized surface plasmon resonance (LSPR) effects. The sensors could simultaneously detect PSA protein biomarker and long noncoding RNA prostate cancer antigen 3 (lncRNA PCA3) with ultrahigh sensitivity and remarkable specificity. Consequently, the proposed dual optical microfibers multiplexed biosensors could detect the PSA protein and lncRNA PCA3 with ultra-low limit-of-detections (LODs) of 3.97 × 10-15 mol/L and 1.56 × 10-14 mol/L in pure phosphorus buffer solution (PBS), respectively, in which the obtained LODs were three orders of magnitude lower than existed state-of-the-art PCa assay technologies. Additionally, the sensors could discriminate target components from complicated physiological environment, that showing noticeable biosensing specificity of the sensors. With good performances of the sensors, they could successfully assay PSA and lncRNA PCA3 in undiluted human serum and urine simultaneously, respectively. Consequently, our proposed multiplexed sensors could real-time high-sensitivity simultaneously detect complicated human samples, that providing a novel valuable approach for the high-accurate diagnosis of early-stage PCa individuals.

MMP-2 Responsive Gold Nanorods Loaded with HSP-70 siRNA for Enhanced Photothermal Tumor Therapy

Gold nanorods (Au NRs) are a valuable photothermal nanomaterial for tumor therapy. However, when treated with Au NRs for photothermal therapy, the expression of heat shock proteins in tumors will increase, which will induce heat resistance in tumor cells and reduce the photothermal therapeutic effect of Au NRs. By RNA interference, the expression of heat shock proteins would be effectively inhibited to improve the efficasy of tumor photothermal therapy. However, deep and noninvasive tissue penetration remains a great obstacle to applying siRNA successfully. Thus, the nanoplatform AGC/HSP-70 siRNA was designed for enhanced photothermal tumor therapy by RNA interference. In the AGC/HSP-70 siRNA complex, the Au-S bond modified the matrix metalloproteinase-2 (MMP-2)-sensitive peptide GPLGLAG on the surface of gold nanorods. Moreover, the natural basic polysaccharide (chitosan) was reacted with the peptide by an amide bond for delivering heat shock protein 70 silencing siRNA (HSP-70 siRNA). Modifying the MMP-2-sensitive linker could cause more Au NRs to accumulate in tumors to exert a photothermal effect and promote the penetration of HSP-70 siRNA and chitosan complexes into deep tumor tissues. In vitro experiments indicated that the enzymolysis of the MMP-2-sensitive linker for AGC/HSP-70 siRNA could promote the cellular uptake and perinuclear distribution of HSP-70 siRNA in tumor cells, which may be due to the smaller size and positive electricity of the complexes. All of these results ensured the efficient gene silencing effect of HSP-70 siRNA to enhance the photothermal therapeutic effect of Au NRs in tumor tissues, as demonstrated by the gene silencing and cellular apoptotic experiments. In vivo experiments further proved that the AGC/HSP-70 siRNA nanoplatform efficiently improved the photothermal effect of Au NRs. In summary, this work proved that AGC/HSP-70 siRNA is a promising drug delivery strategy for enhancing the photothermal therapy of tumors by regulating the photothermal sensitivity of deep tumor cells as well as retaining more Au NRs in tumor tissues, and also provides a novel strategy for tumor photothermal therapy.

Near-infrared-triggered plasmonic regulation and cardiomyocyte-based biosensing system for in vitro bradyarrhythmia treatment

Bradyarrhythmia, a life-threatening cardiovascular disease, is an increasing burden for the healthcare system. Currently, surgery, implanted device, and drug are introduced to treat the bradyarrhythmia in clinical practice. However, these conventional therapeutic strategies suffer from the invasive surgery, power supply, or drug side effect, respectively, hence developing the alternative therapeutic strategy is necessarily imperative. Here, a convenient and effective strategy to treat the bradyarrhythmia is proposed using near-infrared-triggered Au nanorod (NR) based plasmonic photothermal effect (PPE). Moreover, electrophysiology of cardiomyocytes is dynamically monitored by the integrated biosensing-regulating system during and after the treatment. Cardiomyocyte-based bradyarrhythmia recover rhythmic for a long time by regulating plasmonic photothermal effect. Furthermore, the regulatory mechanism is qualitatively investigated to verify the significant thermal stimulation in the recovery process. This study establishes a reliable platform for long-term recording and evaluation of mild photothermal therapy for bradyarrhythmia in vitro, offering an efficient and non-invasive strategy for the potential clinical applications.

Ω-Shaped fiber optic LSPR coated with hybridized nanolayers for tumor cell sensing and photothermal treatment

Circulating tumor cell (CTC) in the blood is the main cause of cancer metastasis for death in cancer patients. It is extremely important for cancer diagnosis at an early stage and treatment to simultaneously detect and kill the CTCs. In this work, a new hybridized nanolayer, namely gold nanoparticle/gold nanorods@ Polydopamine (AuNPs/AuNRs@PDA), was coated on the Ω-shaped fiber optics (Ω-FO) for localized surface plasmonic resonance (LSPR) to perform tumor cell sensing and photothermal treatment (PTT). The PDA nanolayer was formed on a bare fiber optic through the self-polymerization of dopamine under mild conditions. The AuNRs and AuNPs were absorbed on the surface of the PDA nanolayer to form a hybridized nanolayer. The hybridized nanolayer-modified Ω-FO LSPR exhibited a high refractive index sensitivity (RIS) of 37.59 (a.u/RIU) and photothermal conversion efficiency. After being modified with the recognition element of aptamer, the Ω-FO LSPR was used to develop a sensitive and specifical tumor cell sensing. Under the irradiation of near-infrared light (NIR) laser, the Ω-FO LSPR can kill the captured tumor cells with the apoptotic/necrotic rate of 62.6 % and low side-effect for the nontarget cells. The FO LSPR sensor realized the dual functions of CTC sensing and PTT, which provided a new idea for the early diagnosis and treatment of cancer.

Sandwich Layer-Modified Ω-Shaped Fiber-Optic LSPR Enables the Development of an Aptasensor for a Cytosensing-Photothermal Therapy Circuit

The metastasis of cancer cells is a principal cause of morbidity and mortality in cancer. The combination of a cytosensor and photothermal therapy (PTT) cannot completely eliminate cancer cells at one time. Hence, this study aimed to design a localized surface plasmonic resonance (LSPR)-based aptasensor for a circuit of cytosensing-PTT (COCP). This was achieved by coating a novel sandwich layer of polydopamine/gold nanoparticles/polydopamine (PDA/AuNPs/PDA) around the Ω-shaped fiber-optic (Ω-FO). The short-wavelength peak of the sandwich layer with strong resonance exhibited a high refractive index sensitivity (RIS). The modification with the T-shaped aptamer endowed FO-LSPR with unique characteristics of time-dependent sensitivity enhancement behavior for a sensitive cytosensor with the lowest limit of detection (LOD) of 13 cells/mL. The long-wavelength resonance peak in the sandwich layer appears in the near-infrared region. Hence, the rate of increased localized temperature of FO-LSPR was 160 and 30-fold higher than that of the bare and PDA-coated FO, indicating strong photothermal conversion efficiency. After considering the localized temperature distribution around the FO under the flow environment, the FO-LSPR-enabled aptasensor killed 77.6% of cancer cells in simulated blood circulation after five cycles of COCP. The FO-LSPR-enabled aptasensor improved the efficiency of the cytosensor and PTT to effectively kill cancer cells, showing significant potential for application in inhibiting cancer metastasis.

Four-core fiber-based multi-tapered WaveFlex biosensor for rapid detection of Vibrio parahaemolyticus using nanoparticles-enhanced probes

Infections caused by Vibrio parahaemolyticus (V. parahaemolyticus) can be highly fatal, making rapid and sensitive detection of them is essential. A new optical fiber biosensor based on localized surface plasmon resonance (LSPR) phenomenon is developed in this paper. A tapered-in-tapered fiber structure based on MFM is constructed by using four-core fiber (FCF) and multi-mode fiber (MMF) to qualitatively detect different concentrations of V. parahaemolyticus. The sensor successfully excites the LSPR phenomenon and increases the attachment point of biomolecules on the probe surface by fixing gold nanoparticles (AuNPs), molybdenum disulfide nanoparticles (MoS2-NPs) and cerium dioxide nanorods (CeO2-NRs). The functionalization of polyclonal antibodies on the probe surface can improve the specificity of the sensor. The linear detection range of the developed sensor was 1 × 100-1 × 107 CFU/mL, the sensitivity was 1.61 nm/[CFU/mL], and the detection limit was 0.14 CFU/mL. In addition, the reusability, reproducibility, stability, and selectivity of the sensor probe are also tested, which shows that the sensor has great application prospects.

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 Laser-Based Lasso-Shaped Biosensor for High Precision Detection of Cancer Biomarker-CEACAM5 in Serum

Detection of trace tumor markers in blood/serum is essential for the early screening and prognosis of cancer diseases, which requires high sensitivity and specificity of the assays and biosensors. A variety of label-free optical fiber-based biosensors has been developed and yielded great opportunities for Point-of-Care Testing (POCT) of cancer biomarkers. The fiber biosensor, however, suffers from a compromise between the responsivity and stability of the sensing signal, which would deteriorate the sensing performance. In addition, the sophistication of sensor preparation hinders the reproduction and scale-up fabrication. To address these issues, in this study, a straightforward lasso-shaped fiber laser biosensor was proposed for the specific determination of carcinoembryonic antigen (CEA)-related cell adhesion molecules 5 (CEACAM5) protein in serum. Due to the ultra-narrow linewidth of the laser, a very small variation of lasing signal caused by biomolecular bonding can be clearly distinguished via high-resolution spectral analysis. The limit of detection (LOD) of the proposed biosensor could reach 9.6 ng/mL according to the buffer test. The sensing capability was further validated by a human serum-based cancer diagnosis trial, enabling great potential for clinical use. The high reproduction of fabrication allowed the mass production of the sensor and extended its utility to a broader biosensing field.

Recent Advancements of LSPR Fiber-Optic Biosensing: Combination Methods, Structure, and Prospects

Fiber-optic biosensors based on localized surface plasmon resonance (LSPR) have the advantages of great biocompatibility, label-free, strong stability, and real-time monitoring of various analytes. LSPR fiber-optic biosensors have attracted extensive research attention in the fields of environmental science, clinical medicine, disease diagnosis, and food safety. The latest development of LSPR fiber-optic biosensors in recent years has focused on the detection of clinical disease markers and the detection of various toxic substances in the environment and the progress of new sensitization mechanisms in LSPR fiber-optic sensors. Therefore, this paper reviews the LSPR fiber-optic sensors from the aspects of working principle, structure, and application fields in biosensors. According to the structure, the sensor can be divided into three categories: traditional ordinary optical fiber, special shape optical fiber, and specialty optical fiber. The advantages and disadvantages of existing and future LSPR fiber-optic biosensors are discussed in detail. Additionally, the prospect of future development of fiber-optic biosensors based on LSPR is addressed.

T-Shaped Aptamer-Based LSPR Biosensor Using Ω-Shaped Fiber Optic for Rapid Detection of SARS-CoV-2

SARS-CoV-2, especially the variant strains, is rapidly spreading around the world. Rapid detection methods for the virus are crucial for controlling the COVID-19 epidemic. Herein, a localized surface plasmonic resonance (LSPR) biosensor based on Ω-shaped fiber optic (Ω-FO) was developed for dual assays of SARS-CoV-2 monitoring. Due to its strong ability to control the orientation and density, a new T-shaped aptamer exhibits enhanced binding affinity toward N proteins. After being combined on the fiber optic surface, the T-shaped aptamer sensitively captured N proteins of SARS-CoV-2 for a direct assay. Further, core-shell structured gold/silver nanoparticles functionalized with a T-shaped aptamer (apt-Ag@AuNPs) can amplify the signal of N protein detection for a sandwich assay. The real-time analytical feature of the dual assays endows time-dependent sensitivity enhancement behavior, which provides a guideline to save analytical time. With those characteristics, the LSPR biosensor has been successfully used to rapidly identify 39 healthy volunteers and 39 COVID-19 patients infected with the ancestral or variant SARS-CoV-2. With the help of simple pretreatment, we obtain a true negative rate of 100% and a true positive rate of 92.3% with a short analysis time of 45 min using the direct assay. Further, the LSPR biosensor could also broaden the detection application range to the surface of cold-chain foods using a sandwich assay. Thus, the LSPR biosensor based on Ω-FO was demonstrated to have broad application potential to detect SARS-CoV-2 rapidly.

Sandwich method-based sensitivity enhancement of Ω-shaped fiber optic LSPR for time-flexible bacterial detection

The development of rapid and sensitive detection methods for pathogenic bacteria is crucial for the therapy and prevention of related diseases. However, the rapid and ultrasensitive assays are difficult to be realized simultaneously. To solve the problem, a sandwich method based on Ω-shaped fiber optic localized surface resonance (Ω-FOLSPR) was constructed, where poly adenine-tailed aptamer (PolyA-apt) and SH modified gold nanoparticles tags (AuNPs tags) were chosen as the capturing aptamer and amplifying tags, respectively. The small AuNPs were modified on the surface of fiber-optic (FO) rapidly, which saved the preparation time. Then, the PolyA-apt was modified on the AuNPs surface to capture the bacteria effectively due to its ability to adjust the density and conformation of aptamer on the AuNPs surface. Finally, the large AuNPs tags were used to generate intense signal enhancement. It is found that the sandwich method enables the unique characteristic of a time-dependent sensitivity enhancement. Specifically, the LOD of 108.0 CFU/mL and 7.4 CFU/mL was achieved with the analysis time of 10 min and 100 min, respectively. Besides, the Ω-FOLSPR sensor exhibits excellent selectivity against the other bacteria and good performance for detecting the spiked and natural samples. This sandwich method provides a time-flexible strategy due to the combination of effective signal amplification and real-time analysis for bacterial detection, displaying great potential for practical bacterial detection.