Aggregation induced Raman scattering of squaraine dye: Implementation in diagnosis of cervical cancer dysplasia by SERS imaging

Divergent Diazo Approach toward Alkyl 5/4-Hydroxy-3H-benzo[e]indole-4/5-carboxylates

A divergent diazo approach toward alkyl 5/4-hydroxy-3H-benzo[e]indole-4/5-carboxylates has been developed. The reaction of 1,3-diketones with alkyl 2-diazo-3-oxo-3-(2H-azirin-2-yl)propanoates catalyzed by Co(acac)3 or Ni(acac)2 gives various alkyl 3-(1H-pyrrol-2-yl)-2-diazo-3-oxopropanoate in good yields. The latter undergo Wolff rearrangement followed by the 6π-cyclization of transient ketene to form alkyl 5-hydroxy-3H-benzo[e]indole-4-carboxylates bearing various substituents in positions 1, 2, 7, and 8, as well as derivatives of methyl 4-hydroxy-6H-thieno[2,3-e]indole-5-carboxylates and methyl 5-hydroxy-7H-benzo[c]carbazole-6-carboxylate under thermolysis or Rh2(OAc)4 catalysis. Isomeric benzoindoles, alkyl 4-hydroxy-3H-benzo[e]indole-5-carboxylates, have been prepared by Boc-protection of the pyrrole nitrogen of alkyl 3-(1H-pyrrol-2-yl)-2-diazo-3-oxopropanoates followed by an intramolecular formal carbene insertion into the aromatic C-H bond catalyzed by Cu(OTf)2. The hydroxyl group of alkyl 5/4-hydroxy-3H-benzo[e]indole-4/5-carboxylates, through the formation of the corresponding triflates, allows the introduction of various substituents into the 5/4 position of benzo[e]indoles using the cross-coupling reaction and even form a new heterocyclic backbone, benzo[k]pyrrolo[2,3-i]phenanthridine, via a tandem Suzuki reaction/nucleophilic acyl substitution.

Fluorescence-free bis(dithiolene)nickel dyes for surface-enhanced resonance Raman imaging in the second near-infrared window

Second near-infrared window (NIR-II, 1000-1700 nm) imaging is one of the foremost optical imaging techniques. However, surface-enhanced Raman scattering (SERS)-based research in this optical region remains in its infancy, mainly because of a lack of suitable NIR-II Raman reporters. Herein, we report the first example of a nickel dithiolene complex as a NIR-II resonance Raman reporter with intense long wavelength absorption (ε = 9.58 × 104 m-1 cm-1 at 1007 nm), fluorescence-free features and ultrahigh affinity to noble metal surfaces with its eight sulfur atoms. Surface-enhanced resonance Raman scattering nanoprobes constructed with such reporters enable high contrast and highly photostable lymph node imaging far superior to that possible with existing NIR-I and NIR-II SERS nanoprobes. The developed NIR-II nanoprobes allow deep optical penetration (8 mm) as well as in vivo SERS detection of deep-seated microtumors in mice.

Cervical Cancer Detection Techniques: A Chronological Review

Cervical cancer is known as a major health problem globally, with high mortality as well as incidence rates. Over the years, there have been significant advancements in cervical cancer detection techniques, leading to improved accuracy, sensitivity, and specificity. This article provides a chronological review of cervical cancer detection techniques, from the traditional Pap smear test to the latest computer-aided detection (CAD) systems. The traditional method for cervical cancer screening is the Pap smear test. It consists of examining cervical cells under a microscope for abnormalities. However, this method is subjective and may miss precancerous lesions, leading to false negatives and a delayed diagnosis. Therefore, a growing interest has been in shown developing CAD methods to enhance cervical cancer screening. However, the effectiveness and reliability of CAD systems are still being evaluated. A systematic review of the literature was performed using the Scopus database to identify relevant studies on cervical cancer detection techniques published between 1996 and 2022. The search terms used included "(cervix OR cervical) AND (cancer OR tumor) AND (detect* OR diagnosis)". Studies were included if they reported on the development or evaluation of cervical cancer detection techniques, including traditional methods and CAD systems. The results of the review showed that CAD technology for cervical cancer detection has come a long way since it was introduced in the 1990s. Early CAD systems utilized image processing and pattern recognition techniques to analyze digital images of cervical cells, with limited success due to low sensitivity and specificity. In the early 2000s, machine learning (ML) algorithms were introduced to the CAD field for cervical cancer detection, allowing for more accurate and automated analysis of digital images of cervical cells. ML-based CAD systems have shown promise in several studies, with improved sensitivity and specificity reported compared to traditional screening methods. In summary, this chronological review of cervical cancer detection techniques highlights the significant advancements made in this field over the past few decades. ML-based CAD systems have shown promise for improving the accuracy and sensitivity of cervical cancer detection. The Hybrid Intelligent System for Cervical Cancer Diagnosis (HISCCD) and the Automated Cervical Screening System (ACSS) are two of the most promising CAD systems. Still, deeper validation and research are required before being broadly accepted. Continued innovation and collaboration in this field may help enhance cervical cancer detection as well as ultimately reduce the disease's burden on women worldwide.

A clinically feasible diagnostic spectro-histology built on SERS-nanotags for multiplex detection and grading of breast cancer biomarkers

Simultaneous detection of multiple biomarkers is always an obstacle in immunohistochemical (IHC) analysis. Herein, a straightforward spectroscopy-driven histopathologic approach has emerged as a paradigm of Raman-label (RL) nanoparticle probes for multiplex recognition of pertinent biomarkers in heterogeneous breast cancer. The nanoprobes are constructed by sequential incorporation of signature RL and target specific antibodies on gold nanoparticles, which are coined as Raman-Label surface enhanced Raman scattering (RL-SERS)-nanotags to evaluate simultaneous recognition of clinically relevant breast cancer biomarkers i.e., estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor2 (HER2). As a foot-step assessment, breast cancer cell lines having varied expression levels of the triple biomarkers are investigated. Subsequently, the optimized detection strategy using RL-SERS-nanotags is subjected to clinically confirmed, retrospective formalin-fixed paraffin embedded (FFPE) breast cancer tissue samples to fish out the quick response of singleplex, duplex as well as triplex biomarkers in a single tissue specimen by adopting a ratiometric signature RL-SERS analysis which enabled to minimize the false negative and positive results. Significantly, sensitivity and specificity of 95% and 92% for singleplex, 88% and 85% for duplex, and 75% and 67% for triplex biomarker has been achieved by assessing specific Raman fingerprints of the respective SERS-tags. Furthermore, a semi-quantitative evaluation of HER2 grading between 4+/2+/1+ tissue samples was also achieved by the Raman intensity profiling of the SERS-tag, which is fully in agreement with the expensive fluorescent in situ hybridization analysis. Additionally, the practical diagnostic applicability of RL-SERS-tags has been achieved by large area SERS imaging of areas covering 0.5-5 mm2 within 45 min. These findings unveil an accurate, inexpensive and multiplex diagnostic modality envisaging large-scale multi-centric clinical validation.

A SERS/fluorescence dual-mode immuno-nanoprobe for investigating two anti-diabetic drugs on EGFR expressions

A surface-enhanced Raman scattering (SERS)/fluorescence dual-mode nanoprobe was proposed to assess anti-diabetic drug actions from the expression level of the epidermal growth factor receptor (EGFR), which is a significant biomarker of breast cancers. The nanoprobe has a raspberry shape, prepared by coating a dye-doped silica nanosphere with a mass of SERS tags, which gives high gains in fluorescence imaging and SERS measurement. The in situ detection of EGFR on the cell membrane surfaces after drug actions was achieved by using this nanoprobe, and the detection results agree with the enzyme-linked immunosorbent assay (ELISA) kit. Our study suggests that rosiglitazone hydrochloride (RH) may be a potential drug for diabetic patients with breast cancer, while the anti-cancer effect of metformin hydrochloride (MH) is debatable since MH slightly promotes the EGFR expression of MCF-7 cells in this study. This sensing platform endows more feasibility for highly sensitive and accurate feedback of pesticide effects at the membrane protein level.

Sortase E-mediated site-specific immobilization of green fluorescent protein and xylose dehydrogenase on gold nanoparticles

Sortase, a bacterial transpeptidase enzyme, is an attractive tool for protein engineering due to its ability to break a peptide bond at a specific site and then reform a new bond with an incoming nucleophile. Here, we present the immobilization of two recombinant proteins, enhanced green fluorescent protein (eGFP) and xylose dehydrogenase (XylB) over triglycine functionalized PEGylated gold nanoparticles (AuNPs) using C. glutamicum sortase E. For the first time, we used a new class of sortase from a non-pathogenic organism for sortagging. The site-specific conjugation of proteins with LAHTG-tagged sequences on AuNPs via covalent cross-linking was successfully detected by surface-enhanced Raman scattering (SERS) and UV-vis spectral analysis. The sortagging was initially validated by an eGFP model protein and later with the xylose dehydrogenase enzyme. The catalytic activity, stability, and reusability of the immobilized XylB were studied with the bioconversion of xylose to xylonic acid. When compared to the free enzyme, the immobilized XylB was able to retain 80% of its initial activity after four sequential cycles and exhibited no significant variations in instability after each cycle for about 72h. These findings suggest that C. glutamicum sortase could be useful for immobilizing site-specific proteins/enzymes in biotransformation applications for value-added chemical production.

New Bioactive Aromatic Heterocyclic Macromolecules with Monosaccharide Core

1,1,2-trimethyl-1H-benzo[e]indole is an important heterocyclic compound, its available in reasonable price and can easily modified to make a good intermediate for other derivatives. That is quite enough reasons to use as starting material for a new series of compounds with other biomolecules such as monosaccharides after simple modification. The target molecules show biological activity. So, the current work is aiming to improve the activity and the properties of the benzo indole by attaching with a naturally occurring, and biodegradable compounds represented by 2-deoxy-2-amino -d-glucose and 6-deoxy-6-amino-d-glucose to synthesis both mono and di-saccharides derivatives of benzo indole. Two steps synthesis were used for mono-saccharide derivatives and three steps for di-saccharide derivatives, the first is the functionalization of 1,1,2-trimethyl-1H-benzo[e]indole [1] via the reaction with POCl3 to produce 2-(1,1-dimethyl-1H-benzo[e]indol-2(3H)-ylidene) malonaldehyde [2] with two aldehydes reaction centers, while in the second step the latter was coupled with sugar via amino groups to get the two monosaccharide derivatives [3,5], while the disaccharides molecules [4,6] taken one more step with harder conditions to overcome the steric hindrance at the other reaction center. The purity and characterization of the target molecules was confirmed using spectroscopy methods including 1H NMR and 13 NMR. The synthesized compound shows a good biological activity as antibacterial antifungal.

Design and synthesis of gold nanostars-based SERS nanotags for bioimaging applications

Surface-enhanced Raman spectroscopy (SERS) nanotags hold a unique place among bioimaging contrast agents due to their fingerprint-like spectra, which provide one of the highest degrees of detection specificity. However, in order to achieve a sufficiently high signal intensity, targeting capabilities, and biocompatibility, all components of nanotags must be rationally designed and tailored to a specific application. Design parameters include fine-tuning the properties of the plasmonic core as well as optimizing the choice of Raman reporter molecule, surface coating, and targeting moieties for the intended application. This review introduces readers to the principles of SERS nanotag design and discusses both established and emerging protocols of their synthesis, with a specific focus on the construction of SERS nanotags in the context of bioimaging and theranostics.

Cascade Reaction of 2-Naphthols and Azirines: One-Pot Synthesis of C-3 Naphthol-Substituted Benzo[e]indoles

A copper-catalyzed annulation of 3-aryl-2H-azirines with 2-naphthols has been developed for the rapid assembly of C-3-naphthol-substituted benzo[e]indoles in one pot. This cascade reaction was realized through dearomatic nucleophilic ring opening of azirine, intramolecular cyclization, and oxidative cross-dehydrogenative coupling to furnish the important unreported π-expanded naphthol/benzo[e]indole biaryls.

A computational probe granting insight into intra and inter-stacking interactions in squaraine dye derivatives

In order to decipher structure function relationships regarding the optoelectronic properties of organic functional materials, two sets of anilinosquaraine dye derivatives were analysed computationally. 2,4-Bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl]squaraine exhibits orthorhombic and monoclinic polymorphs (motif-1 and motif-2) in bulk and spin coated films, respectively, and concomitant J- and H-aggregate spectral features. In the second set, in spite of variation in the n-alkyl chain of the anilinosquaraine derivatives (n-propyl vs. n-butyl; motif-3 and motif-4), both acquired triclinic morphology and intermolecular charge transfer had been identified as the origin of their panchromaticity. The differences between these motifs were closely inspected at the theoretical level including geometrical parameters, internal reorganization energies, charge transfer integrals, drift mobilities, interaction energies and lattice energies along with a comprehensive Hirshfeld surface analysis. A correlation was established between C⋯C type intra-stack interactions with the observed red-shifted absorption patterns in the order motif-1 > motif-3 > motif-4. Hydrophobic interactions, π-π interactions and hydrogen bonds were found to influence the crystal packing patterns and concomitantly the overall molecule planarity and thereby the extent of π-bond delocalization/resonance. Insights into intra-stack and inter-stack interactions based on crystal packing effects are provided, which support and potentially guide the experimentalists' key ideas for shaping and encompassing the applications of promising squaraine derivative materials.

Elucidating Raman Image-Guided Differential Recognition of Clinically Confirmed Grades of Cervical Exfoliated Cells by Dual Biomarker-Appended SERS-Tag

Ultrasensitive detection of cancer biomarkers via single-cell analysis through Raman imaging is an impending approach that modulates the possibility of early diagnosis. Cervical cancer is one such type that can be monitored for a sufficiently long period toward invasive cancer phenotype. Herein, we report a surface-enhanced Raman scattering (SERS) nanotag (SERS-tag) for the simultaneous detection of p16/K-i67, a dual biomarker persisting in the progression of squamous cell carcinoma of human cervix. A nanoflower-shaped SERS-tag, constituted of hybrid gold nanostar with silver tips to achieve maximum fingerprint enhancement from the incorporated reporter molecule, was further functionalized with the cocktail monoclonal antibodies against p16/K-i67. The recognition by the SERS-tag was first validated in cervical squamous cell carcinoma cell line SiHa as a foot-step study and subsequently implemented to different grades of clinically confirmed exfoliated cells including normal cell (NC), high-grade intra-epithelial lesion (HC), and squamous cell carcinoma (CC) samples of the cervix. Precise Raman mapped images were constituted based on the average intensity gradient of the signature Raman peaks arising from different grades of exfoliated cells. We observed a distinct intensity hike of around 10-fold in the single dysplastic HC and CC samples in comparison to NC specimen, which clearly justify the prevalence of p16/Ki-67. The synthesized probe is able to map the abnormal cells within 20 min with high reproducibility and stability for 1 mm × 1 mm mapping area with good contrast. Amidst the challenges in Raman image-guided modality, the technique was further complemented with the gold standard immunocytochemistry (ICC) dual staining analysis. Even though both are time-consuming techniques, tedious steps can be avoided and real-time readout can be achieved using the SERS mapping unlike immunocytochemistry technique. Therefore, the newly developed Raman image-guided SERS imaging emphasizes the approach of uplifting of SERS in practical utility with further improvement for clinical applications for cervical cancer detection in future.

Raman Imaging: An Impending Approach Towards Cancer Diagnosis

In accordance with the recent studies, Raman spectroscopy is well experimented as a highly sensitive analytical and imaging technique in biomedical research, mainly for various disease diagnosis including cancer. In comparison with other imaging modalities, Raman spectroscopy facilitate numerous assistances owing to its low background signal, immense spatial resolution, high chemical specificity, multiplexing capability, excellent photo stability and non-invasive detection capability. In cancer diagnosis Raman imaging intervened as a promising investigative tool to provide molecular level information to differentiate the cancerous vs non-cancerous cells, tissues and even in body fluids. Anciently, spontaneous Raman scattering is very feeble due to its low signal intensity and long acquisition time but new advanced techniques like coherent Raman scattering (CRS) and surface enhanced Raman scattering (SERS) gradually superseded these issues. So, the present review focuses on the recent developments and applications of Raman spectroscopy-based imaging techniques for cancer diagnosis.

Surface charge modulates the internalization vs. penetration of gold nanoparticles: comprehensive scrutiny on monolayer cancer cells, multicellular spheroids and solid tumors by SERS modality

Precise control over the dynamics of nanoparticles (NPs) in a tumor microenvironment is highly warranted for the development of an efficient nanotheranostic agent. Even though inductively coupled plasma mass spectrometry can provide a quantitative assessment regarding the uptake efficiency of metal NPs, enumeration of deep tissue penetration capacity remains as a challenge. Herein, we have demonstrated an accurate tracking of the uptake efficiency and penetration phenomenon of gold nanoparticles (AuNPs: 40-50 nm) with respect to three different surface charges in monolayer (2D) cells, multicellular spheroids (3D) and in vivo tumors by surface-enhanced Raman spectroscopy (SERS). While positively charged AuNPs showed around two-fold increased internalization in monolayer cells, SERS-tag-based line scanning on multi-layered tumor spheroids illustrated almost nine-fold superior penetration capability with negatively charged AuNPs. Further, the enhanced solid tumor distribution contributed by the negatively charged AuNPs could appreciably escalate its clinical utility in cancer management.

Corrosion prevention of commercial alloys by air-water interface grown, edge on oriented, ultrathin squaraine film

Copper is one of the most demanded commercial metal/alloys in world market. The demand for copper in industries such as electrical, electronics, automobile, telecommunications, defence, etc. as well as in daily life has escalated in the recent years due to its versatile physical and chemical properties. However destruction of copper surface by any means, preferably corrosion, can limit its vast application. For protection from corrosion, various techniques are used to coat metal substrates with passivating materials. These techniques are either complex as well as expensive, or provide incomplete protection in acid media. To address these issues, floating film transfer method (FFTM) is utilized in this work for obtaining ultrathin film of squaraine (passivating molecule) as well as their easy and fast transfer over copper substrate. The squaraine film is deposited on copper substrate in layers, viz., 1 to 4 layers. The corrosion behavior is examined in 0.1 M HCl using electrochemical techniques as well as surface characterization techniques, which portray that copper corrosion is hampered in harmony with the layers deposited. Nearly 40% corrosion protection is reached for copper coated with 1 layer of squaraine. However, the protection is amplified up to 98% with 4 layers of squaraine, which clearly substantiates the supremacy of this coating method over reported methods of protection. This technique and the material (squaraine) are both for the first time being used in the field of corrosion protection. The easy growth of ultrathin film at air-water interface as well as its rapid transfer over substrate promotes use of FFTM for efficient corrosion protection on industrial scale.

Correlation of surface-enhanced Raman scattering (SERS) with the surface density of gold nanoparticles: evaluation of the critical number of SERS tags for a detectable signal

The use of plasmonic nanotags based on the surface-enhanced Raman scattering (SERS) effect is highly promising for several applications in analytical chemistry, biotechnological assays and nanomedicine. To this end, a crucial parameter is the minimum number of SERS tags that allows for the collection of intense Raman signals under real operating conditions. Here, SERS Au nanotags (AuNTs) based on clustered gold nanoparticles are deposited on a substrate and analyzed in the same region using Raman spectroscopy and transmission electron microscopy. In this way, the Raman spectra and the surface density of the SERS tags are correlated directly, showing that 1 tag/µm² is enough to generate an intense signal above the noise level at 633 nm with an excitation power of only 0.65 mW and an acquisition time of just 1 s with a 50× objective. The AuNT density can be even lower than 1 tag/µm² when the acquisition time is extended to 10 s, but must be increased to 3 tags/µm² when a 20× objective is employed under the same excitation conditions. In addition, in order to observe a linear response, it was found that 10 SERS AuNTs inside the probed area are required. These findings indicate that a better signal-to-noise ratio requires high-magnification optics, while linearity versus tag number can be improved by using low-magnification optics or a high tag density. In general the suitability of plasmonic SERS labels for ultrasensitive analytical and biomedical applications is evident.

Probe design for super-multiplexed vibrational imaging

Optical microscopy has served biomedical research for decades due to its high temporal and spatial resolutions. Among various optical imaging techniques, fluorescence imaging offers superb sensitivity down to single molecule level but its multiplexing capacity is limited by intrinsically broad bandwidth. To simultaneously capture a vast number of targets, the newly emerging vibrational microscopy technique draws increasing attention as vibration spectroscopy features narrow transition linewidth. Nonetheless, unlike fluorophores that have been studied for centuries, a systematic investigation on vibrational probes is underemphasized. Herein, we reviewed some of the recent developments of vibrational probes for multiplex imaging applications, particularly those serving stimulated Raman scattering (SRS) microscopy, which is one of the most promising vibrational imaging techniques. We wish to summarize the general guidelines for developing bioorthogonal vibrational probes with high sensitivity, chemical specificity and most importantly, tunability to fulfill super-multiplexed optical imaging. Future directions to significantly improve the performance are also discussed.

Gold nanostructures as cancer theranostic probe: promises and hurdles

Gold nanostructures (GNSts) have emerged as substitute for conventional contrast agents in imaging techniques and therapeutic probes due to their tunable surface plasmon resonance and optical properties in near-infrared region. Thus GNSts provide platform for the amalgamation of diagnosis and treatment (theranostics) into a single molecule for a more precise treatment. Hence, the article talks about the application of GNSts in imaging techniques and provide a holistic view on differently shaped GNSts in cancer theranostics. However, with promises GNSts also face various hurdles for their use as theranostic probe which are primarily associated with toxicity. Finally, the article attempts to discuss the challenges faced by GNSts and the way ahead that need to be traversed to place them in nanomedicine.

Recent advances in merging photonic crystals and plasmonics for bioanalytical applications

Photonic crystals (PhCs) and plasmonic nanostructures offer the unprecedented capability to control the interaction of light and biomolecules at the nanoscale. Based on PhC and plasmonic phenomena, a variety of analytical techniques have been demonstrated and successfully implemented in many fields, such as biological sciences, clinical diagnosis, drug discovery, and environmental monitoring. During the past decades, PhC and plasmonic technologies have progressed in parallel with their pros and cons. The merging of photonic crystals with plasmonics will significantly improve biosensor performances and enlarge the linear detection range of analytical targets. Here, we review the state-of-the-art biosensors that combine PhC and plasmonic nanomaterials for quantitative analysis. The optical mechanisms of PhCs, plasmonic crystals, and metal nanoparticles (NPs) are presented, along with their integration and potential applications. By explaining the optical coupling of photonic crystals and plasmonics, the review manifests how PhC-plasmonic hybrid biosensors can achieve the advantages, including high sensitivity, low cost, and short assay time as well. The review also discusses the challenges and future opportunities in this fascinating field.

Bimodal detection of carbon dioxide using fluorescent molecular aggregates

Fluorescent aggregates of a cyano-substituted phenylenevinylene derivative (R-1) have been used as a bimodal probe for the easy and fast detection of CO₂.

Nanoparticles and intracellular applications of surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectrocopy (SERS) offers ultrasensitive vibrational fingerprinting at the nanoscale. Its non-destructive nature affords an ideal tool for interrogation of the intracellular environment, detecting the localisation of biomolecules, delivery and monitoring of therapeutics and for characterisation of complex cellular processes at the molecular level. Innovations in nanotechnology have produced a wide selection of novel, purpose-built plasmonic nanostructures capable of high SERS enhancement for intracellular probing while microfluidic technologies are being utilised to reproducibly synthesise nanoparticle (NP) probes at large scale and in high throughput. Sophisticated multivariate analysis techniques unlock the wealth of previously unattainable biomolecular information contained within large and multidimensional SERS datasets. Thus, with suitable combination of experimental techniques and analytics, SERS boasts enormous potential for cell based assays and to expand our understanding of the intracellular environment. In this review we trace the pathway to utilisation of nanomaterials for intracellular SERS. Thus we review and assess nanoparticle synthesis methods, their toxicity and cell interactions before presenting significant developments in intracellular SERS methodologies and how identified challenges can be addressed.

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.

Highly Sensitive Squaraine-Based Water-Soluble Far-Red/Near-Infrared Chromofluorogenic Thiophenol Probe

A squaraine-based far-red/near-infrared fluorescent probe (SQ-DNBS) was exploited for thiophenol detection. SQ-DNBS is a colorimetric and "off-on" fluorometric dual-channel "naked-eye" chemosensor showing high selectivity, high sensitivity (detection limit: 9.9 nM), and rapid response to thiophenol in aqueous solution. SQ-DNBS also can be used in practical applications for the detection of thiophenol in water samples. Photophysical and spectral characterization results revealed that the probing mechanism of SQ-DNBS toward thiophenol lies in the thiolate-mediated cleavage reaction. Our discovery demonstrates the potential of the arylmethylene-squaraine skeleton as a promising fluorophore unit to construct high-performance far-red/near-infrared chemosensors.

Recent advances in biosensor development for the detection of cancer biomarkers

Cancer is the second largest disease throughout the world with an increasing mortality rate over the past few years. The patient's survival rate is uncertain due to the limitations of cancer diagnosis and therapy. Early diagnosis of cancer is decisive for its successful treatment. A biomarker-based cancer diagnosis may significantly improve the early diagnosis and subsequent treatment. Biosensors play a crucial role in the detection of biomarkers as they are easy to use, portable, and can do analysis in real time. This review describes various biosensors designed for detecting nucleic acid and protein-based cancer biomarkers for cancer diagnosis. It mainly lays emphasis on different approaches to use electrochemical, optical, and mass-based transduction systems in cancer biomarker detection. It also highlights the analytical performances of various biosensor designs concerning cancer biomarkers in detail.

Multiplex bioassays encoded by photonic crystal beads and SERS nanotags

Multiplex bioassays have drawn more and more attention for the development of novel analytical techniques. Herein, we used photonic crystal (PC) and surface enhanced Raman scattering (SERS) as two encoding elements in different modes for the dual encoding of multiplex bioassays. In practice, PC beads and SERS nanotags act as carriers and labels, respectively, for the multiplex detection of antigens in a sandwich format. Except for the amplified capacity by two encoding modes, we also demonstrated that fine stability, low background and high sensitivity were realized for the quantitative analysis of multiple analytes, which holds great promise in biomedical applications like protein biomarker analysis.

New Insight of Tetraphenylethylene-based Raman Signatures for Targeted SERS Nanoprobe Construction Toward Prostate Cancer Cell Detection

We have designed and synthesized novel tetraphenylethylene (TPE) appended organic fluorogens and unfold their unique Raman fingerprinting reflected by surface-enhanced Raman scattering (SERS) upon adsorption on nanoroughened gold surface as a new insight in addition to their prevalent aggregation-induced emission (AIE) and aggregation-caused quenching (ACQ) phenomena. A series of five TPE analogues has been synthesized consisting of different electron donors such as (1) indoline with propyl (TPE-In), (2) indoline with lipoic acid (TPE-In-L), (3) indoline with Boc-protected propyl amine (TPE-In-Boc), (4) benzothaizole (TPE-B), and (5) quinaldine (TPE-Q). Interestingly, all five TPE analogues produced multiplexing Raman signal pattern, out of which TPE-In-Boc showed a significant increase in signal intensity in the fingerprint region. An efficient SERS nanoprobe has been constructed using gold nanoparticles as SERS substrate, and the TPE-In as the Raman reporter, which conjugated with a specific peptide substrate, Cys-Ser-Lys-Leu-Gln-OH, well-known for the recognition of prostate-specific antigen (PSA). The designated nanoprobe TPE-In-PSA@Au acted as SERS "ON/OFF" probe in peace with the vicinity of PSA protease, which distinctly recognizes PSA expression with a limit of detection of 0.5 ng in SERS platform. Furthermore, TPE-In-PSA@Au nanoprobe was efficiently recognized the overexpressed PSA in human LNCaP cells, which can be visualized through SERS spectral analysis and SERS mapping.

Biomimetic synthesis of highly biocompatible gold nanoparticles with amino acid-dithiocarbamate as a precursor for SERS imaging

Amino acid-dithiocarbamate (amino acid-DTC) was developed as both the reductant and ligand stabilizer for biomimetic synthesis of gold nanoparticles (AuNPs), which served as an excellent surface-enhanced Raman scattering (SERS) contrast nanoprobe for cell imaging. Glycine (Gly), glutamic acid (Glu), and histidine (His) with different isoelectric points were chosen as representative amino acid candidates to synthesize corresponding amino acid-DTC compounds through mixing with carbon disulfide (CS2), respectively. The pyrogenic decomposition of amino acid-DTC initiated the reduction synthesis of AuNPs, and the strong coordinating dithiocarbamate group of amino acid-DTC served as a stabilizer that grafted onto the surface of the AuNPs, which rendered the as-prepared nanoparticles a negative surface charge and high colloidal stability. MTT cell viability assay demonstrated that the biomimetic AuNPs possessed neglectful toxicity to the human hepatoma cell, which guaranteed them good biocompatibility for biomedical application. Meanwhile, the biomimetic AuNPs showed a strong SERS effect with an enhancement factor of 9.8 × 10(5) for the sensing of Rhodamine 6G, and two distinct Raman peaks located at 1363 and 1509 cm(-1) could be clearly observed in the cell-imaging experiments. Therefore, biomimetic AuNPs can be explored as an excellent SERS contrast nanoprobe for biomedical imaging, and the amino acid-DTC mediated synthesis of the AuNPs has a great potential in bio-engineering and biomedical imaging applications.

Rough surface Au@Ag core-shell nanoparticles to fabricating high sensitivity SERS immunochromatographic sensors

Immunochromatographic sensors (ICSs) are inexpensive, simple, portable, and robust, thus making ICSs commonplace in clinical diagnoses, food testing, and environmental monitoring. However, commonly used gold nanoparticles (AuNPs) ICSs have low sensitivity. Therefore, we developed highly sensitive surface enhanced Raman scattering (SERS) ICSs. To enhance the sensitivity of SERS ICSs, rough surface core-shell Au@Ag nanoparticles (RSAu@AgNPs) were prepared by coating silver on the surface of gold nanoflowers (AuNFs). Then these nanoparticles were used as SERS substrate in the SERS ICSs, after which the SERS ICSs were implemented to detect haemoglobin and heavy metal cadmium ion (Cd(2+)). The limit of detection (LOD) of the SERS ICSs for detecting haemoglobin was 8 ng/mL, and the linear range of the SERS ICSs was from 31.3 to 2000 ng/mL. The LOD of the SERS ICSs for detecting Cd(2+) was 0.05 ng/mL and the linear analysis range was from 0.05 to 25 ng/mL. The cross reactivity of the SERS ICSs was studied and results showed that the SERS ICSs exhibited highly specific for detection of haemoglobin and Cd(2+), respectively. The SERS ICSs were then used to detect haemoglobin (spiked in serum and in stool) and Cd(2+) (spiked in tap water, river water, and soil leaching water), and the results showed high recovery. These characteristics indicated that SERS ICSs were ideal tools for clinical diagnosis and environmental pollution monitoring.