Bio-sensing with butterfly wings: naturally occurring nano-structures for SERS-based malaria parasite detection

Nanoplasmonic biosensors for environmental sustainability and human health

Monitoring the health conditions of the environment and humans is essential for ensuring human well-being, promoting global health, and achieving sustainability. Innovative biosensors are crucial in accurately monitoring health conditions, uncovering the hidden connections between the environment and human well-being, and understanding how environmental factors trigger autoimmune diseases, neurodegenerative diseases, and infectious diseases. This review evaluates the use of nanoplasmonic biosensors that can monitor environmental health and human diseases according to target analytes of different sizes and scales, providing valuable insights for preventive medicine. We begin by explaining the fundamental principles and mechanisms of nanoplasmonic biosensors. We investigate the potential of nanoplasmonic techniques for detecting various biological molecules, extracellular vesicles (EVs), pathogens, and cells. We also explore the possibility of wearable nanoplasmonic biosensors to monitor the physiological network and healthy connectivity of humans, animals, plants, and organisms. This review will guide the design of next-generation nanoplasmonic biosensors to advance sustainable global healthcare for humans, the environment, and the planet.

Malaria: biochemical, physiological, diagnostic, and therapeutic updates

Background

Malaria has been appraised as a significant vector-borne parasitic disease with grave morbidity and high-rate mortality. Several challenges have been confronting the efficient diagnosis and treatment of malaria.

Method

Google Scholar, PubMed, Web of Science, and the Egyptian Knowledge Bank (EKB) were all used to gather articles.

Results

Diverse biochemical and physiological indices can mirror complicated malaria e.g., hypoglycemia, dyslipidemia, elevated renal and hepatic functions in addition to the lower antioxidant capacity that does not only destroy the parasite but also induces endothelial damage. Multiple trials have been conducted to improve recent points of care in malaria involving biosensors, lap on-chip, and microdevices technology. Regarding recent therapeutic trials, chemical falcipain inhibitors and plant extracts with anti-plasmodial activities are presented. Moreover, antimalaria nano-medicine and the emergence of nanocarrier (either active or passive) in drug transportation are promising. The combination therapeutic trials e.g., amodiaquine + artemether + lumefantrine are presented to safely counterbalance the emerging drug resistance in addition to the Tafenoquine as a new anti-relapse therapy.

Conclusion

Recognizing the pathophysiology indices potentiate diagnosis of malaria. The new points of care can smartly manipulate the biochemical and hematological alterations for a more sensitive and specific diagnosis of malaria. Nano-medicine appeared promising. Chemical and plant extracts remain points of research.

The Laboratory Diagnosis of Malaria: A Focus on the Diagnostic Assays in Non-Endemic Areas

Even if malaria is rare in Europe, it is a medical emergency and programs for its control should ensure both an early diagnosis and a prompt treatment within 24-48 h from the onset of the symptoms. The increasing number of imported malaria cases as well as the risk of the reintroduction of autochthonous cases encouraged laboratories in non-endemic countries to adopt diagnostic methods/algorithms. Microscopy remains the gold standard, but with limitations. Rapid diagnostic tests have greatly expanded the ability to diagnose malaria for rapid results due to simplicity and low cost, but they lack sensitivity and specificity. PCR-based assays provide more relevant information but need well-trained technicians. As reported in the World Health Organization Global Technical Strategy for Malaria 2016-2030, the development of point-of-care testing is important for the improvement of diagnosis with beneficial consequences for prompt/accurate treatment and for preventing the spread of the disease. Despite their limitations, diagnostic methods contribute to the decline of malaria mortality. Recently, evidence suggested that artificial intelligence could be utilized for assisting pathologists in malaria diagnosis.

Bioinspired superhydrophobic SERS substrates for machine learning assisted miRNA detection in complex biomatrix below femtomolar limit

Surface-enhanced Raman spectroscopy (SERS) is an analytical method with high potential in the field of medicine. The design of SERS substrates, based on specific morphology and/or chemical modification, allow the recognition of the presence of specific analytes with precision close to a single-molecule detection limit. However, the SERS analysis of real samples is significantly complicated by the presence of a large number of "minor" molecules that can shield the signal from the target analyte and make it impossible to determine it in practice. In this work, an advanced SERS approach was used for the detection of cancer-related miRNA-21 in blood plasma, used as a molecular model background. The approach was based on the combination of the biomimetic plasmon-active SERS substrate, its tuned surface chemistry and advanced SERS data analysis, making use of artificial machine learning. In the first step, biomimetic SERS substrates were created using a butterfly wing as a starting template. The substrates were covered by thin Au layer and covalently grafted with hydrophobic chemical moieties to introduce superhydrophobic and water-adhesive properties. The self-concentration of the analyte on the substrates was achieved by minimizing the contact area between the analyte drop and the substrate, which is facilitated by surface superhydrophobicity and additionally enhanced by drop evaporation on the flipped over substrate. Due to the presence of cancer miRNA and blood plasma background, the measured SERS spectra represent a complex of interfering peaks. Thus, their interpretation was carried out using a specially trained machine learning model. As a result, reliable and repeatable quantitative detection of miRNAs below the femtomolar level (up to 10-16 M) on the background of human blood plasma becomes possible.

A magnetic field augmented ultra-thin layer chromatography coupled surface enhanced Raman spectroscopy separation of hemozoin from bacterial mixture

Malaria is considered as one the most widespread disease with highest possibility of co-infection at all levels of the disease prognosis. Rapid detection and discrimination of malaria from other co-infections remains a challenge. Hemozoin is a metabolic biproduct of malaraia possessing paramagnetic property due to presence of iron at its centre. Here, we report a label free, rapid and highly sensitive magnetic field based ultra-thin layer chromatography (UTLC) coupled with surface enhanced Raman spectroscopy (SERS) technique for detection and separation of hemozoin from a bacterial mixture. Highly optimized silver nanorods chip fabricated using glancing angle deposition (GLAD) is explored for the UTLC-SERS separation. These chips possessing channel like characteristic and high surface to the volume ratio serve as excellent UTLC plates. The magnetic nature of hemozoin has been exploited for its separation from the mixture of P. aeruginosa (Gram-negative) and S. aureus (Gram-positive) by allocating a 0.6 T magnet over the UTLC flow setup. The solvent front migrated approximately to a distance of 13 mm from the sample point due to the magnetic environment. Spatially resolved SERS data was collected along the mobile phase and separation of mixture was confirmed. Further, staining of hemozoin, P. aeruginosa and S. aureus was done using methylene blue, acridine orange and rhodamine 6 G respectively. The separation was confirmed for the stained analytes. The present developed method provides plate height as low as 18 µm and hemozoin detection limit as <10 parasites/mL. Therefore, we establish a highly specific and sensitive technique capable of separating small amounts of bioanalytes, aiding in the removal of co-infections from the disease at a very early stage of infection.

SERS determination of sodium saccharin content on the tipping paper of cigarettes using AgNP substrates prepared with a USB-power supply device

A novel magnetic agitating heater powered by a USB port has been developed and applied to synthesize silver colloid substrate for surface-enhanced Raman scattering (SERS) detection of sodium saccharin content on the tipping paper of cigarettes. The heater device allows the convenient synthesis of the Ag colloid, and the reaction can be completed on-site in 15 min under mild conditions. The on-site synthesis of SERS substrate effectively avoided the need for storage and concerns regarding the poor stability and short lifespan of colloid substrates. The results demonstrated that the substrate obtained with the device could achieve SERS detection of Rhodamine 6G (R6G) at as low as 10-9 mol L-1 while maintaining a stable intensity with a relative standard deviation (RSD) of 5.52% (n = 5). Using the prepared substrate at the optimal conditions, the limit of detection of sodium saccharin (SS) was 1 mg L-1. By introducing an internal standard KSCN, a linear relationship was observed between the relative intensity at 708 cm-1 and the concentration of the SS in a range of 20-100 mg L-1 (R2 = 0.98). With the developed method, SS was directly extracted from the cigarette paper by immersing it in water, and the extracted solution was subsequently detected. The quantitative spike-recoveries were in the range of 95.5-116.7%, with RSD between 2.3-12.6%. The whole detection procedure including the on-site substrate preparation, took only about 30 min. This work opens new avenues for colloidal synthesis, and the detection method of SS on the cigarette paper also holds great promise in food safety applications.

Nanomaterials meet surface-enhanced Raman scattering towards enhanced clinical diagnosis: a review

Surface-enhanced Raman scattering (SERS) is a very promising tool for the direct detection of biomarkers for the diagnosis of i.e., cancer and pathogens. Yet, current SERS strategies are hampered by non-specific interactions with co-existing substances in the biological matrices and the difficulties of obtaining molecular fingerprint information from the complex vibrational spectrum. Raman signal enhancement is necessary, along with convenient surface modification and machine-based learning to address the former issues. This review aims to describe recent advances and prospects in SERS-based approaches for cancer and pathogens diagnosis. First, direct SERS strategies for key biomarker sensing, including the use of substrates such as plasmonic, semiconductor structures, and 3D order nanostructures for signal enhancement will be discussed. Secondly, we will illustrate recent advances for indirect diagnosis using active nanomaterials, Raman reporters, and specific capture elements as SERS tags. Thirdly, critical challenges for translating the potential of the SERS sensing techniques into clinical applications via machine learning and portable instrumentation will be described. The unique nature and integrated sensing capabilities of SERS provide great promise for early cancer diagnosis or fast pathogens detection, reducing sanitary costs but most importantly allowing disease prevention and decreasing mortality rates.

Discriminant Analysis PCA-LDA Assisted Surface-Enhanced Raman Spectroscopy for Direct Identification of Malaria-Infected Red Blood Cells

Various methods for detecting malaria have been developed in recent years, each with its own set of advantages. These methods include microscopic, antigen-based, and molecular-based analysis of blood samples. This study aimed to develop a new, alternative procedure for clinical use by using a large data set of surface-enhanced Raman spectra to distinguish normal and infected red blood cells. PCA-LDA algorithms were used to produce models for separating P. falciparum (3D7)-infected red blood cells and normal red blood cells based on their Raman spectra. Both average normalized spectra and spectral imaging were considered. However, these initial spectra could hardly differentiate normal cells from the infected cells. Then, discrimination analysis was applied to assist in the classification and visualization of the different spectral data sets. The results showed a clear separation in the PCA-LDA coordinate. A blind test was also carried out to evaluate the efficiency of the PCA-LDA separation model and achieved a prediction accuracy of up to 80%. Considering that the PCA-LDA separation accuracy will improve when a larger set of training data is incorporated into the existing database, the proposed method could be highly effective for the identification of malaria-infected red blood cells.

Plasmonic nanosensors for point-of-care biomarker detection

Advancement of materials along with their fascinating properties play increasingly important role in facilitating the rapid progress in medicine. An excellent example is the recent development of biosensors based on nanomaterials that induce surface plasmon effect for screening biomarkers of various diseases ranging from cancer to Covid-19. The recent global pandemic re-confirmed the trend of real-time diagnosis in public health to be in point-of-care (POC) settings that can screen interested biomarkers at home, or literally anywhere else, at any time. Plasmonic biosensors, thanks to its versatile designs and extraordinary sensitivities, can be scaled into small and portable devices for POC diagnostic tools. In the meantime, efforts are being made to speed up, simplify and lower the cost of the signal readout process including converting the conventional heavy laboratory instruments into lightweight handheld devices. This article reviews the recent progress on the design of plasmonic nanomaterial-based biosensors for biomarker detection with a perspective of POC applications. After briefly introducing the plasmonic detection working mechanisms and devices, the selected highlights in the field focusing on the technology's design including nanomaterials development, structure assembly, and target applications are presented and analyzed. In parallel, discussions on the sensor's current or potential applicability in POC diagnosis are provided. Finally, challenges and opportunities in plasmonic biosensor for biomarker detection, such as the current Covid-19 pandemic and its testing using plasmonic biosensor and incorporation of machine learning algorithms are discussed.

Selenium Vacancies and Synergistic Effect of Near- and Far-Field-Enabled Ultrasensitive Surface-Enhanced Raman-Scattering-Active Substrates for Malaria Detection

Defect engineering with the active control of defect states brings remarkable enhancement on surface-enhanced Raman scattering (SERS) by magnifying semiconductor-molecule interaction. Such light-trapping architectures can increase the light path length, which promotes photon-analytes interactions and further improves the SERS sensitivity. However, by far the reported semiconductor SERS-active substrates based on these strategies are often nonuniform and commonly in the form of isolated laminates or random clusters, which limit their reliability and stability for practical applications. Herein, we develop self-grown single-crystalline "V-shape" SnSe_2-x (SnSe_1.5, SnSe_1.75, SnSe₂) nanoflake arrays (SnSe_2-x NFAs) with controlled selenium vacancies over large-area (10 cm × 10 cm) for ultrahigh-sensitivity SERS. First-principles density functional theory (DFT) is used to calculate the band gap and the electronic density of states (DOS). Based on the Herzberg-Teller theory regarding the vibronic coupling, the results of theoretical calculation reveal that the downshift of band edge and high DOS of SnSe_1.75 can effectively enhance the vibronic coupling within the SnSe_1.75-R6G system, which in turn enhances the photoinduced charge transfer resonance and contributes to the SERS activity with a remarkable enhancement factor of 1.68 × 10⁷. Furthermore, we propose and demonstrate ultrasensitive (10^-15 M for R6G), uniform, and reliable SERS substrates by forming SnSe_1.75 NFAs/Au heterostructures via a facile Au evaporation process. We attribute the superior performance of our SnSe_1.75 NFAs/Au heterostructures to the following reasons: (1) selenium vacancies and (2) synergistic effect of the near and far fields. In addition, we successfully build a detection platform to achieve rapid (∼15 min for the whole process), antibody-free, in situ, and reliable early malaria detection (100% detection rate for 10 samples with 160 points) in whole blood, and molecular hemozoin (<100/mL) can be detected. Our approach not only provides an efficient technique to obtain large-area, uniform, and reliable SERS-active substrates but also offers a substantial impact on addressing practical issues in many application scenarios such as the detection of insect-borne infectious diseases.

Review of Microdevices for Hemozoin-Based Malaria Detection

Despite being preventable and treatable, malaria still puts almost half of the world's population at risk. Thus, prompt, accurate and sensitive malaria diagnosis is crucial for disease control and elimination. Optical microscopy and immuno-rapid tests are the standard malaria diagnostic methods in the field. However, these are time-consuming and fail to detect low-level parasitemia. Biosensors and lab-on-a-chip devices, as reported to different applications, usually offer high sensitivity, specificity, and ease of use at the point of care. Thus, these can be explored as an alternative for malaria diagnosis. Alongside malaria infection inside the human red blood cells, parasites consume host hemoglobin generating the hemozoin crystal as a by-product. Hemozoin is produced in all parasite species either in symptomatic and asymptomatic individuals. Furthermore, hemozoin crystals are produced as the parasites invade the red blood cells and their content relates to disease progression. Hemozoin is, therefore, a unique indicator of infection, being used as a malaria biomarker. Herein, the so-far developed biosensors and lab-on-a-chip devices aiming for malaria detection by targeting hemozoin as a biomarker are reviewed and discussed to fulfil all the medical demands for malaria management towards elimination.

A review of surface-enhanced Raman spectroscopy in pathological processes

With the continuous growth of the human population and new challenges in the quality of life, it is more important than ever to diagnose diseases and pathologies with high accuracy, sensitivity and in different scenarios from medical implants to the operation room. Although conventional methods of diagnosis revolutionized healthcare, alternative analytical methods are making their way out of academic labs into clinics. In this regard, surface-enhanced Raman spectroscopy (SERS) developed immensely with its capability to achieve single-molecule sensitivity and high-specificity in the last two decades, and now it is well on its way to join the arsenal of physicians. This review discusses how SERS is becoming an essential tool for the clinical investigation of pathologies including inflammation, infections, necrosis/apoptosis, hypoxia, and tumors. We critically discuss the strategies reported so far in nanoparticle assembly, functionalization, non-metallic substrates, colloidal solutions and how these techniques improve SERS characteristics during pathology diagnoses like sensitivity, selectivity, and detection limit. Moreover, it is crucial to introduce the most recent developments and future perspectives of SERS as a biomedical analytical method. We finally discuss the challenges that remain as bottlenecks for a routine SERS implementation in the medical room from in vitro to in vivo applications. The review showcases the adaptability and versatility of SERS to resolve pathological processes by covering various experimental and analytical methods and the specific spectral features and analysis results achieved by these methods.

The Future in Sensing Technologies for Malaria Surveillance: A Review of Hemozoin-Based Diagnosis

Early and effective malaria diagnosis is vital to control the disease spread and to prevent the emergence of severe cases and death. Currently, malaria diagnosis relies on optical microscopy and immuno-rapid tests; however, these require a drop of blood, are time-consuming, or are not specific and sensitive enough for reliable detection of low-level parasitaemia. Thus, there is an urge for simpler, prompt, and accurate alternative diagnostic methods. Particularly, hemozoin has been increasingly recognized as an attractive biomarker for malaria detection. As the disease proliferates, parasites digest host hemoglobin, in the process releasing toxic haem that is detoxified into an insoluble crystal, the hemozoin, which accumulates along with infection progression. Given its magnetic, optical, and acoustic unique features, hemozoin has been explored for new label-free diagnostic methods. Thereby, herein, we review the hemozoin-based malaria detection methods and critically discuss their challenges and potential for the development of an ideal diagnostic device.

Surface-Enhanced Raman Spectroscopy for Molecule Characterization: HIM Investigation into Sources of SERS Activity of Silver-Coated Butterfly Scales

Surface-enhanced Raman spectroscopy (SERS) is a powerful technique for obtaining structural information of molecules in solution at low concentrations. While commercial SERS substrates are available, high costs prevent their wide-spread use in the medical field. One solution is to prepare requisite noble metal nanostructures exploiting natural nanostructures. As an example of biomimetic approaches, butterfly wing scales with their intricate nanostructures have been found to exhibit exquisite SERS activity when coated with silver. Selecting appropriate scales from particular butterfly species and depositing silver of certain thicknesses leads to significant SERS activity. For morphological observations we used scanning electron microscopes as well as a helium ion microscope, highly suitable for morphological characterization of poorly conducting samples. In this paper, we describe a protocol for carrying out SERS measurements based on butterfly wing scales and demonstrate its LOD with a common Raman reporter, rhodamine 6 G. We also emphasize what special care is necessary in such measurements. We also try to shed light on what makes scales work as SERS substrates by carefully modifying the original nanostructures. Such a study allows us to either use scales directly as a raw material for SERS substrate or provides an insight as to what nanostructures need to be recreated for synthetic SERS substrates.

Rapid quantification of the malaria biomarker hemozoin by improved biocatalytically initiated precipitation atom transfer radical polymerizations

The fight against tropical diseases such as malaria requires the development of innovative biosensing techniques. Diagnostics must be rapid and robust to ensure prompt case management and to avoid further transmission. The malaria biomarker hemozoin can catalyze atom transfer radical polymerizations (ATRP), which we exploit in a polymerization-amplified biosensing assay for hemozoin based on the precipitation polymerization of N-isopropyl acrylamide (NIPAAm). The reaction conditions are systematically investigated using synthetic hemozoin to gain fundamental understanding of the involved reactions and to greatly reduce the amplification time, while maintaining the sensitivity of the assay. The use of excess ascorbate allows oxygen to be consumed in situ but leads to the formation of reactive oxygen species and to the decomposition of the initiator 2-hydroxyethyl 2-bromoisobutyrate (HEBIB). Addition of sodium dodecyl sulfate (SDS) and pyruvate results in better differentiation between the blank and hemozoin-containing samples. Optimized reaction conditions (including reagents, pH, and temperature) reduce the amplification time from 37 ± 5 min to 3 ± 0.5 min while maintaining a low limit of detection of 1.06 ng mL-1. The short amplification time brings the precipitation polymerization assay a step closer to a point-of-care diagnostic device for malaria. Future efforts will be dedicated to the isolation of hemozoin from clinical samples.

Antibody-free rapid diagnosis of malaria in whole blood with surface-enhanced Raman Spectroscopy using Nanostructured Gold Substrate

PURPOSE

The aim of this study is to establish a rapid antibody-free diagnostic method of malaria infection with Plasmodium falciparum and Plasmodium vivax in whole blood with Surface-enhanced Raman Spectroscopy using Nanostructured Gold Substrate.

MATERIALS AND METHODS

The blood samples collected from patients were first lysed and centrifuged before dropping on the gold nano-structure (AuNS) substrate. Malaria diagnosis was performed by detecting Raman peaks from Surface Enhanced Raman Spectroscopy (SERS) with a 532 nm laser excitation.

RESULTS

Raman peaks at 1370 cm-1, 1570 cm-1, and 1627 cm-1, known to have high specificity against interference from other mosquito-borne diseases such as Dengue and West Nile virus infection, were selected as the fingerprint markers associated with P. falciparum and P. vivax infection. The limit of detection was 10-5 dilution, corresponding to the concentration of parasitized blood cells of 100/mL. A total number of 25 clinical samples, including 5 from patients with P. falciparum infection, 10 with P. vivax infection and 10 from healthy volunteers, were evaluated to support its clinical practical use. The whole assay on malaria detection took 30 min to complete.

CONCLUSIONS

While the samples analyzed in this work have strong clinical relevance, we have clearly demonstrated that sensitive malaria detection using AuNS-SERS is a practical direction for rapid in-field diagnosis of malaria infection.

Guided cellular orientation concurrently with cell density gradient on butterfly wings

A simple method to create guided cellular orientation is illustrated by assembling fibroblasts on the dorsal side of M. menelaus wings. Moreover, by inserting the wing into tendon fibroblasts suspension at a tilt angle, guided cellular orientation concurrently with the cell density gradient is formed on the butterfly wings.

Recent Advancement in the Surface-Enhanced Raman Spectroscopy-Based Biosensors for Infectious Disease Diagnosis

Diagnosis is the key component in disease elimination to improve global health. However, there is a tremendous need for diagnostic innovation for neglected tropical diseases that largely consist of mosquito-borne infections and bacterial infections. Early diagnosis of these infectious diseases is critical but challenging because the biomarkers are present at low concentrations, demanding bioanalytical techniques that can deliver high sensitivity with ensured specificity. Owing to the plasmonic nanomaterials-enabled high detection sensitivities, even up to single molecules, surface-enhanced Raman spectroscopy (SERS) has gained attention as an optical analytical tool for early disease biomarker detection. In this mini-review, we highlight the SERS-based assay development tailored to detect key types of biomarkers for mosquito-borne and bacterial infections. We discuss in detail the variations of SERS-based techniques that have developed to afford qualitative and quantitative disease biomarker detection in a more accurate, affordable, and field-transferable manner. Current and emerging challenges in the advancement of SERS-based technologies from the proof-of-concept phase to the point-of-care phase are also briefly discussed.

Hemozoin-catalyzed precipitation polymerization as an assay for malaria diagnosis

Methods to diagnose malaria are of paramount interest to eradicate the disease. Current methods have severe limitations, as they are either costly or not sensitive enough to detect low levels of parasitemia. Here we report an ultrasensitive, yet low-resource chemical assay for the detection and quantification of hemozoin, a biomarker of all Plasmodium species. Solubilized hemozoin catalyzes the atom transfer radical polymerization of N-isopropylacrylamide above the lower critical solution temperature of poly(N-isopropylacrylamide). The solution becomes turbid, which can be observed by naked eye and quantified by UV-visible spectroscopy. The rate of turbidity increase is proportional to the concentration of hemozoin, with a detection limit of 0.85 ng mL-1. Malaria parasites in human blood can be detected down to 10 infected red blood cells μL-1. The assay could potentially be applied as a point-of-care test. The signal-amplification of an analyte by biocatalytic precipitation polymerization represents a powerful approach in biosensing.

Inorganic Complexes and Metal-Based Nanomaterials for Infectious Disease Diagnostics

Infectious diseases claim millions of lives each year. Robust and accurate diagnostics are essential tools for identifying those who are at risk and in need of treatment in low-resource settings. Inorganic complexes and metal-based nanomaterials continue to drive the development of diagnostic platforms and strategies that enable infectious disease detection in low-resource settings. In this review, we highlight works from the past 20 years in which inorganic chemistry and nanotechnology were implemented in each of the core components that make up a diagnostic test. First, we present how inorganic biomarkers and their properties are leveraged for infectious disease detection. In the following section, we detail metal-based technologies that have been employed for sample preparation and biomarker isolation from sample matrices. We then describe how inorganic- and nanomaterial-based probes have been utilized in point-of-care diagnostics for signal generation. The following section discusses instrumentation for signal readout in resource-limited settings. Next, we highlight the detection of nucleic acids at the point of care as an emerging application of inorganic chemistry. Lastly, we consider the challenges that remain for translation of the aforementioned diagnostic platforms to low-resource settings.

Nanomaterial-based SERS sensing technology for biomedical application

Over the past few years, nanomaterial-based surface-enhanced Raman scattering (SERS) detection has emerged as a new exciting field in which theoretical and experimental studies of the structure and function of nanomaterials have become a focus.

Raman Spectroscopy to Diagnose Alzheimer's Disease and Dementia with Lewy Bodies in Blood

Accurate identification of Alzheimer's disease (AD) is still of major clinical importance considering the current lack of noninvasive and low-cost diagnostic approaches. Detection of early stage AD is particularly desirable as it would allow early intervention or recruitment of patients into clinical trials. There is also an unmet need for discrimination of AD from dementia with Lewy bodies (DLB), as many cases of the latter are misdiagnosed as AD. Biomarkers based on a simple blood test would be useful in research and clinical practice. Raman spectroscopy has been implemented to analyze blood plasma of a cohort that consisted of early stage AD, late-stage AD, DLB, and healthy controls. Classification algorithms achieved high accuracy for the different groups: early stage AD vs healthy with 84% sensitivity, 86% specificity; late-stage AD vs healthy with 84% sensitivity, 77% specificity; DLB vs healthy with 83% sensitivity, 87% specificity; early-stage AD vs DLB with 81% sensitivity, 88% specificity; late-stage AD vs DLB with 90% sensitivity, 93% specificity; and lastly, early-stage AD vs late-stage AD 66% sensitivity and 83% specificity. G-score values were also estimated between 74% and 91%, demonstrating that the overall performance of the classification model was satisfactory. The wavenumbers responsible for differentiation were assigned to important biomolecules, which can serve as a panel of biomarkers. These results suggest a cost-effective, blood-based test for neurodegeneration in dementias.

Analysis of Biomolecules Based on the Surface Enhanced Raman Spectroscopy

Analyzing biomolecules is essential for disease diagnostics, food safety inspection, environmental monitoring and pharmaceutical development. Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for detecting biomolecules due to its high sensitivity, rapidness and specificity in identifying molecular structures. This review focuses on the SERS analysis of biomolecules originated from humans, animals, plants and microorganisms, combined with nanomaterials as SERS substrates and nanotags. Recent advances in SERS detection of target molecules were summarized with different detection strategies including label-free and label-mediated types. This comprehensive and critical summary of SERS analysis of biomolecules might help researchers from different scientific backgrounds spark new ideas and proposals.

Exploring the margins of SERS in practical domain: An emerging diagnostic modality for modern biomedical applications

Excellent multiplexing capability, molecular specificity, high sensitivity and the potential of resolving complex molecular level biological compositions augmented the diagnostic modality of surface-enhanced Raman scattering (SERS) in biology and medicine. While maintaining all the merits of classical Raman spectroscopy, SERS provides a more sensitive and selective detection and quantification platform. Non-invasive, chemically specific and spatially resolved analysis facilitates the exploration of SERS-based nano probes in diagnostic and theranostic applications with improved clinical outcomes compared to the currently available so called state-of-art technologies. Adequate knowledge on the mechanism and properties of SERS based nano probes are inevitable in utilizing the full potential of this modality for biomedical applications. The safety and efficiency of metal nanoparticles and Raman reporters have to be critically evaluated for the successful translation of SERS in to clinics. In this context, the present review attempts to give a comprehensive overview about the selected medical, biomedical and allied applications of SERS while highlighting recent and relevant outcomes ranging from simple detection platforms to complicated clinical applications.

High resolution FTIR imaging provides automated discrimination and detection of single malaria parasite infected erythrocytes on glass

New highly sensitive tools for malaria diagnostics are urgently needed to enable the detection of infection in asymptomatic carriers and patients with low parasitemia. In pursuit of a highly sensitive diagnostic tool that can identify parasite infections at the single cell level, we have been exploring Fourier transform infrared (FTIR) microscopy using a Focal Plane Array (FPA) imaging detector. Here we report for the first time the application of a new optic configuration developed by Agilent that incorporates 25× condenser and objective Cassegrain optics with a high numerical aperture (NA = 0.81) along with additional high magnification optics within the microscope to provide 0.66 micron pixel resolution (total IR system magnification of 61×) to diagnose malaria parasites at the single cell level on a conventional glass microscope slide. The high quality images clearly resolve the parasite's digestive vacuole demonstrating sub-cellular resolution using this approach. Moreover, we have developed an algorithm that first detects the cells in the infrared image, and secondly extracts the average spectrum. The average spectrum is then run through a model based on Partial Least Squares-Discriminant Analysis (PLS-DA), which diagnoses unequivocally the infected from normal cells. The high quality images, and the fact this measurement can be achieved without a synchrotron source on a conventional glass slide, shows promise as a potential gold standard for malaria detection at the single cell level.

Multifunctional Ag-decorated g-C3N4 nanosheets as recyclable SERS substrates for CV and RhB detection

In this study, g-C₃N₄/Ag hybrid nanostructures were fabricated by facilely decorating silver nanoparticles on atmosphere-treated g-C₃N₄ and served as efficient SERS-active substrates. The observed significant SERS enhancement of crystal violet (CV) molecules on g-C₃N₄/Ag could be attributed to the high ability to concentrate target molecules through π–π stacking interactions and the near-field enhancement caused by the boosting SPR effect of the Ag NPs. The atmosphere and calcination time have a considerable impact on the SERS enhancement effect of the g-C₃N₄/Ag substrate. Furthermore, it took only 10 min to degrade dye molecules under visible light, and after 6 cycles the g-C₃N₄/Ag substrates still maintained sensitive SERS activity. This research indicates that g-C₃N₄/Ag hybrids can be applied as reusable SERS substrates.

In this study, g-C₃N₄/Ag hybrid nanostructures were fabricated by facilely decorating silver nanoparticles on atmosphere-treated g-C₃N₄ and served as efficient SERS-active substrates.

Chitin-Based Anisotropic Nanostructures of Butterfly Wings for Regulating Cells Orientation

In recent years, multiple types of substrates have been applied for regulating cell orientation. Among them, surface topography patterns with grooves or ridges have been widely utilizing for cell culturing. However, this construction is still complicated, low cost-effective and exhibits some technological limitations with either "top-down" or "bottom-up" approaches. Here, a simple and green method was developed by utilizing butterfly wings (Morpho menelaus, Papilio ulysses telegonus and Ornithoptera croesus lydius) with natural anisotropic nanostructures to generate cell alignment. A two-step chemical treatment was proposed to achieve more hydrophilic butterfly wings preceding cell culturing. Furthermore, calcein acetoxymethyl ester (Calcein-AM) staining and Methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay results demonstrated the appropriate viability of NIH-3T3 fibroblast cells on those butterfly wings. Moreover, the cells displayed a high degree of alignment in each specimen of these wings. We anticipate that those originating from natural butterfly wings will pose important applications for tissue engineering.

Direct detection of malaria infected red blood cells by surface enhanced Raman spectroscopy

Surface enhanced Raman spectra (SERS) of normal red blood cells (RBCs) and Plasmodium falciparum infected RBCs (iRBCs) at different post invasion time were obtained based on silver nanorod array substrates. Distinct spectral differences were observed due to the cell membrane modification of RBCs during malaria infection. The SERS spectra of ring stage iRBCs had a characteristic Raman peak at Δv=1599cm(-1) as compared to those of normal RBCs, while the trophozoite and schizoid stages had identical SERS spectra with a characteristic peak at Δv=723cm(-1), which is significantly different from ring stage iRBCs, consistent with ongoing modification of the iRBC membrane. Since ring stage iRBCs of P. falciparum are found circulating in blood, such a difference provides a new strategy for rapid malaria detection. The limit of detection as well as the ability to detect a mixed iRBC and RBC solution was also investigated.

From near-infrared and Raman to surface-enhanced Raman spectroscopy: progress, limitations and perspectives in bioanalysis

Over recent decades, spreading environmental concern entailed the expansion of green chemistry analytical tools. Vibrational spectroscopy, belonging to this class of analytical tool, is particularly interesting taking into account its numerous advantages such as fast data acquisition and no sample preparation. In this context, near-infrared, Raman and mainly surface-enhanced Raman spectroscopy (SERS) have thus gained interest in many fields including bioanalysis. The two former techniques only ensure the analysis of concentrated compounds in simple matrices, whereas the emergence of SERS improved the performances of vibrational spectroscopy to very sensitive and selective analyses. Complex SERS substrates were also developed enabling biomarker measurements, paving the way for SERS immunoassays. Therefore, in this paper, the strengths and weaknesses of these techniques will be highlighted with a focus on recent progress.

Novel molecular diagnostic tools for malaria elimination: a review of options from the point of view of high-throughput and applicability in resource limited settings

As malaria transmission continues to decrease, an increasing number of countries will enter pre-elimination and elimination. To interrupt transmission, changes in control strategies are likely to require more accurate identification of all carriers of Plasmodium parasites, both symptomatic and asymptomatic, using diagnostic tools that are highly sensitive, high throughput and with fast turnaround times preferably performed in local health service settings. Currently available immunochromatographic lateral flow rapid diagnostic tests and field microscopy are unlikely to consistently detect infections at parasite densities less than 100 parasites/µL making them insufficiently sensitive for detecting all carriers. Molecular diagnostic platforms, such as PCR and LAMP, are currently available in reference laboratories, but at a cost both financially and in turnaround time. This review describes the recent progress in developing molecular diagnostic tools in terms of their capacity for high throughput and potential for performance in non-reference laboratories for malaria elimination.

Towards ultrasensitive malaria diagnosis using surface enhanced Raman spectroscopy

We report two methods of surface enhanced Raman spectroscopy (SERS) for hemozoin detection in malaria infected human blood. In the first method, silver nanoparticles were synthesized separately and then mixed with lysed blood; while in the second method, silver nanoparticles were synthesized directly inside the parasites of Plasmodium falciparum. It was observed that the first method yields a smaller variation in SERS measurements and stronger correlation between the estimated contribution of hemozoin and the parasitemia level, which is preferred for the quantification of the parasitemia level. In contrast, the second method yields a higher sensitivity to a low parasitemia level thus could be more effective in the early malaria diagnosis to determine whether a given blood sample is positive.

Developing and understanding biofluid vibrational spectroscopy: a critical review

Biofluid vibrational spectroscopy, a promising tool for rapid disease diagnosis.

Surface-enhanced resonance Raman scattering of hemoproteins and those in complicated biological systems

The SERRS spectra of heme are influenced by structural changes, orientation, and selective adsorption on the Ag surface.