Nanoparticle labels in immunosensing using optical detection methods

Functionalized Single Crystal Perovskite Materials for SERS and Their Potential Detection Applications

Recent advances in detection and diagnostic tools have improved understanding and identification of plant physiological and biochemical processes. Effective and safe Surface Enhanced Raman Spectroscopy (SERS) can find objects quickly and accurately. Raman enhancement amplifies the signal by 1014-1015 to accurately quantify plant metabolites at the molecular level. This paper shows how to use functionalized perovskite substrates for SERS. These perovskite substrates have lots of surface area, intense Raman scattering, and high sensitivity and specificity. These properties eliminate sample matrix component interference. This study identified research gaps on perovskite substrates' effectiveness, precision, and efficiency in biological metabolite detection compared to conventional substrates. This article details the synthesis and use of functionalized perovskites for plant metabolites measurement. It analyzes their pros and cons in this context. The manuscript analyzes perovskite-based SERS substrates, including single-crystalline perovskites with enhanced optoelectronic properties. This manuscript aims to identify this study gap by comprehensively reviewing the literature and using it to investigate plant metabolite detection in future studies.

Optical nanomaterial-based detection of biomarkers in liquid biopsy

Liquid biopsy, which is a minimally invasive procedure as an alternative to tissue biopsy, has been introduced as a new diagnostic/prognostic measure. By screening disease-related markers from the blood or other biofluids, it promises early diagnosis, timely prognostication, and effective treatment of the diseases. However, there will be a long way until its realization due to its conceptual and practical challenges. The biomarkers detected by liquid biopsy, such as circulating tumor cell (CTC) and circulating tumor DNA (ctDNA), are extraordinarily rare and often obscured by an abundance of normal cellular components, necessitating ultra-sensitive and accurate detection methods for the advancement of liquid biopsy techniques. Optical biosensors based on nanomaterials open an important opportunity in liquid biopsy because of their enhanced sensing performance with simple and practical properties. In this review article, we summarized recent innovations in optical nanomaterials to demonstrate the sensitive detection of protein, peptide, ctDNA, miRNA, exosome, and CTCs. Each study prepares the optical nanomaterials with a tailored design to enhance the sensing performance and to meet the requirements of each biomarker. The unique optical characteristics of metallic nanoparticles (NPs), quantum dots, upconversion NPs, silica NPs, polymeric NPs, and carbon nanomaterials are exploited for sensitive detection mechanisms. These recent advances in liquid biopsy using optical nanomaterials give us an opportunity to overcome challenging issues and provide a resource for understanding the unknown characteristics of the biomarkers as well as the mechanism of the disease.

Immunosensors-The Future of Pathogen Real-Time Detection

Pathogens and their toxins can cause various diseases of different severity. Some of them may be fatal, and therefore early diagnosis and suitable treatment is essential. There are numerous available methods used for their rapid screening. Conventional laboratory-based techniques such as culturing, enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) are dominant. However, culturing still remains the "gold standard" for their identification. These methods have many advantages, including high sensitivity and selectivity, but also numerous limitations, such as long experiment-time, costly instrumentation, and the need for well-qualified personnel to operate the equipment. All these existing limitations are the reasons for the continuous search for a new solutions in the field of bacteria identification. For years, research has been focusing on the use of immunosensors in various types of toxin- and pathogen-detection. Compared to the conventional methods, immunosensors do not require well-trained personnel. What is more, immunosensors are quick, highly selective and sensitive, and possess the potential to significantly improve the pathogen and toxin diagnostic-processes. There is a very important potential use for them in various transport systems, where the risk of contamination by bioagents is very high. In this paper, the advances in the field of immunosensor usage in pathogenic microorganism- and toxin-detection, are described.

Lateral Flow Immunoassays for SARS-CoV-2

The continued circulation of SARS-CoV-2 virus in different parts of the world opens up the possibility for more virulent variants to evolve even as the coronavirus disease 2019 transitions from pandemic to endemic. Highly transmissible and virulent variants may seed new disruptive epidemic waves that can easily put the healthcare system under tremendous pressure. Despite various nucleic acid-based diagnostic tests that are now commercially available, the wide applications of these tests are largely hampered by specialized equipment requirements that may not be readily available, accessible and affordable in less developed countries or in low resource settings. Hence, the availability of lateral flow immunoassays (LFIs), which can serve as a diagnostic tool by detecting SARS-CoV-2 antigen or as a serological tool by measuring host immune response, is highly appealing. LFI is rapid, low cost, equipment-free, scalable for mass production and ideal for point-of-care settings. In this review, we first summarize the principle and assay format of these LFIs with emphasis on those that were granted emergency use authorization by the US Food and Drug Administration followed by discussion on the specimen type, marker selection and assay performance. We conclude with an overview of challenges and future perspective of LFI applications.

Hyperspectral dark field optical microscopy for orientational imaging of a single plasmonic nanocube using a physics-based learning method

Rotational dynamics at the molecular level could provide additional data regarding protein diffusion and cytoskeleton formation at the cellular level. Due to the isotropic emission pattern of fluorescence molecules, it is challenging to extract rotational information from them during imaging. Metal nanoparticles show a polarization-dependent response and could be used for sensing rotational motion. Nanoparticles as an orientation sensing probe offer bio-compatibility and robustness against photo-blinking and photo-bleaching compared to conventional fluorescent molecules. Previously, asymmetric geometrical structures such as nanorods have been used for orientational imaging. Here, we show orientational imaging of symmetric geometrical structures such as 100 nm isolated silver nanocubes by coupling a hyperspectral detector and a focused ion beam (FIB)-fabricated correlating substrate. More than 100 nanocubes are analyzed to confirm spectral shifts in the scattering spectra due to variations in the orientation of the nanocubes with respect to the incoming light. Results are further validated using finite-difference time-domain simulations. Our observations suggest a novel strategy for high-throughput orientation imaging of nanoparticles.

Tracking the concentration of Al3+ in the aqueous system up to nanomolar range using modified biopolymer chitosan based fluorophore

The paper reports the development of biopolymer chitosan based fluorophore for selective detection of Al3+ in aqueous streams. Fluorescence sensing based on the change in the photophysical properties of the...

Monatomic Iodine Dielectric Layer for Multimodal Optical Spectroscopy of Dye Molecules on Metal Surfaces

Fluorescence and Raman scattering spectroscopies have been used in various research fields such as chemistry, electrochemistry, and biochemistry because they can easily obtain detailed information about molecules at interfaces with visible light. In particular, multimodal fluorescence and Raman scattering spectroscopy have recently attracted significant attention, which enables us to distinguish chemical species and their electronic states that are important for expressing various functions. However, a special strategy is required to perform simultaneous measurements because the cross sections of fluorescence and Raman scattering differ by as much as ∼10¹⁴. In this study, we propose a method for the simultaneous measurement of dye molecules on a metal surface using a monatomic layer of iodine as the dielectric layer. The method is based on adequately quenching the photoexcited state of the molecules near the metal surface to weaken the fluorescence intensity and using the resonance effect to increase the Raman signal. We have validated this concept by experiments with insulating layers of different thicknesses and dye molecules of different chemical structures. The proposed multimodal strategy paves the way for various applications such as catalytic chemistry and electrochemistry, where the adsorption structure and electronic states of molecular species near the metal surface determine functionalities.

Laser-induced breakdown spectroscopy as a readout method for immunocytochemistry with upconversion nanoparticles

Immunohistochemistry (IHC) and immunocytochemistry (ICC) are widely used to identify cancerous cells within tissues and cell cultures. Even though the optical microscopy evaluation is considered the gold standard, the limited range of useful labels and narrow multiplexing capabilities create an imminent need for alternative readout techniques. Laser-induced breakdown spectroscopy (LIBS) enables large-scale multi-elemental analysis of the surface of biological samples, e.g., thin section or cell pellet. It is, therefore, a potential alternative for IHC and ICC readout of various labels or tags (Tag-LIBS approach). Here, we introduce Tag-LIBS as a method for the specific determination of HER2 biomarker. The cell pellets were labeled with streptavidin-conjugated upconversion nanoparticles (UCNP) through a primary anti-HER2 antibody and a biotinylated secondary antibody. The LIBS scanning enabled detecting the characteristic elemental signature of yttrium as a principal constituent of UCNP, thus indirectly providing a reliable way to differentiate between HER2-positive BT-474 cells and HER2-negative MDA-MB-231 cells. The comparison of results with upconversion optical microscopy and luminescence intensity scanning confirmed that LIBS is a promising alternative for the IHC and ICC readout.

Recent progress on developing of plasmon biosensing of tumor biomarkers: Efficient method towards early stage recognition of cancer

Cancer is the second most extended disease with an improved death rate over the past several time. Due to the restrictions of cancer analysis methods, the patient's real survival rate is unknown. Therefore, early stage diagnosis of cancer is crucial for its strong detection. Bio-analysis based on biomarkers may help to overcome the problem Biosensors with high sensitivity and specificity, low-cost, high analysis speed and minimum limit of detection are practical alternatives for laboratory tests. Surface plasmon resonance (SPR) is reaching a maturity level sufficient for their application in detection and determination cancer biomarkers in clinical samples. This review discusses main concepts and performance characteristics of SPR biosensor. Mainly, it focuses on newly emerged enhanced SPR biosensors towards high-throughput and ultrasensitive screening of cancer biomarkers such as PSA, α-fetoprotein, CEA, CA125, CA 15-3, HER2, ctDNA, ALCAM, hCG, VEGF, TNF, Interleukin, IFN-γ, CD24, CD44, Ferritin, COLIV using labeling processes with focusing on the future application in biomedical research and clinical diagnosis. This article reviews current status of the field, showcasing a series of early successes in the application of SPR for clinical bioanalysis of cancer related biomolecules and detailing a series of considerations regarding sensing schemes, exposing issues with analysis in biofluids, while providing an outlook of the challenges currently associated with plasmonic materials, bioreceptor selection, microfluidics, and validation of a clinical bioassay for applying SPR biosensors to clinical samples. Research opportunities are proposed to further advance the field and transition SPR biosensors from research proof-of-concept stage to actual clinical usage.

Advances in Optical Single-Molecule Detection: En Route to Supersensitive Bioaffinity Assays

The ability to detect low concentrations of analytes and in particular low-abundance biomarkers is of fundamental importance, e.g., for early-stage disease diagnosis. The prospect of reaching the ultimate limit of detection has driven the development of single-molecule bioaffinity assays. While many review articles have highlighted the potentials of single-molecule technologies for analytical and diagnostic applications, these technologies are not as widespread in real-world applications as one should expect. This Review provides a theoretical background on single-molecule-or better digital-assays to critically assess their potential compared to traditional analog assays. Selected examples from the literature include bioaffinity assays for the detection of biomolecules such as proteins, nucleic acids, and viruses. The structure of the Review highlights the versatility of optical single-molecule labeling techniques, including enzymatic amplification, molecular labels, and innovative nanomaterials.

Electronic classification of barcoded particles for multiplexed detection using supervised machine learning analysis

Wearable biosensors are of great interest in recent years due to their potential in health related applications. Multiplex biomarker analysis is needed in wearable devices to improve the sensitivity and reliability. Electronic barcoding of micro-particles has the possibility to enable multiplexed biomarker analysis. Compared with traditional optical and plasmonic methods for barcoding, electronically barcoded particles can be classified using ultra-compact electronic readout platforms. Nano-electronic barcoding works by depositing a thin layer of oxide on the top half of a micro-particle. The thickness and dielectric property of the oxide layer can be tuned to modulate the frequency dependent impedance signature of the particles. A one to one correspondence between a target biomarker and each barcoded particle can potentially be established using this technique. The barcoded particles could be tested with wearable devices to enable multiplex analysis for portable point-of-care diagnostics and real-time monitoring. In this work, we fabricated nine barcoded particles by forming oxide layers of different thicknesses and different dielectric materials using atomic layer deposition and assessed the ability to accurately classify particle barcodes using multi-frequency impedance cytometry in conjunction with supervised machine learning.

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.

High sensitivity and label-free oligonucleotides detection using photonic bandgap sensing structures biofunctionalized with molecular beacon probes

A label-free sensor, based on the combination of silicon photonic bandgap (PBG) structures with immobilized molecular beacon (MB) probes, is experimentally developed. Complementary target oligonucleotides are specifically recognized through hybridization with the MB probes on the surface of the sensing structure. This combination of PBG sensing structures and MB probes demonstrates an extremely high sensitivity without the need for complex PCR-based amplification or labelling methods.

Noble metal nanostructures in optical biosensors: Basics, and their introduction to anti-doping detection

Nanotechnology has illustrated significant potentials in biomolecular-sensing applications; particularly its introduction to anti-doping detection is of great importance. Illicit recreational drugs, substances that can be potentially abused, and drugs with dosage limitations according to the prohibited lists announced by the World Antidoping Agency (WADA) are becoming of increasing interest to forensic chemists. In this review, the theoretical principles of optical biosensors based on noble metal nanoparticles, and the transduction mechanism of commonly-applied plasmonic biosensors are covered. We review different classes of recently-developed plasmonic biosensors for analytic determination and quantification of illicit drugs in anti-doping applications. The important classes of illicit drugs include anabolic steroids, opioids, stimulants, and peptide hormones. The main emphasis is on the advantages that noble metal nano-particles bring to optical biosensors for signal enhancement and the development of highly sensitive (label-free) biosensors. In the near future, such optical biosensors may be an invaluable substitute for conventional anti-doping detection methods such as chromatography-based approaches, and may even be commercialized for routine anti-doping tests.

Investigating Colorimetric Protein Array Assay Schemes for Detection of Recurrence of Bladder Cancer

A colorimetric microarray for the multiplexed detection of recurrence of bladder cancer including protein markers interleukin-8 (IL8), decorin (DCN), and vascular endothelial growth factor (VEGF) was established to enable easy and cheap read-out by a simple office scanner paving the way for quick therapy monitoring at doctors' offices. The chip is based on the principle of a sandwich immunoassay and was optimized prior to multiplexing using IL8 as a model marker. Six different colorimetric assay formats were evaluated using a detection antibody (dAB) labeled with (I) gold (Au) nanoparticles (NPs), (II) carbon NPs, (III) oxidized carbon NPs, and a biotinylated dAB in combination with (IV) neutravidin-carbon, (V) streptavidin (strp)-gold, and (VI) strp-horseradish peroxidase (HRP). Assay Format (III) worked best for NP-based detection and showed a low background while the enzymatic approach, using 3,3',5,5'-tetramethylbenzidine (TMB) substrate, led to the most intense signals with good reproducibility. Both assay formats showed consistent spot morphology as well as detection limits lower than 15 ng/L IL8 and were thus applied for the multiplexed detection of IL8, DCN, and VEGF in synthetic urine. Colorimetric detection in urine (1:3) yields reaction signals and measurement ranges well comparable with detection in the assay buffer, as well as excellent data reproducibility as indicated by the coefficient of variation (CV 5-9%).

Encapsulation-Stabilized, Europium Containing Nanoparticle as a Probe for Time-Resolved luminescence Detection of Cardiac Troponin I

The use of a robust optical signaling probe with a high signal-to-noise ratio is important in the development of immunoassays. Lanthanide chelates are a promising material for this purpose, which provide time-resolved luminescence (TRL) due to their large Stokes shift and long luminescence lifetime. From this, they have attracted considerable interest in the in vitro diagnostics field. However, the direct use of lanthanide chelates is limited because their luminescent signal can be easily affected by various quenchers. To overcome this drawback, strategies that rely on the entrapment of lanthanide chelates inside nanoparticles, thereby enabling the protection of the lanthanide chelate from water, have been reported. However, the poor stability of the lanthanide-entrapped nanoparticles results in a significant fluctuation in TRL signal intensity, and this still remains a challenging issue. To address this, we have developed a Lanthanide chelate-Encapsulated Silica Nano Particle (LESNP) as a new immunosensing probe. In this approach, the lanthanide chelate is covalently crosslinked within the silane monomer during the silica nanoparticle formation. The resulting LESNP is physically stable and retains TRL properties of the parent lanthanide chelate. Using the probe, a highly sensitive, sandwich-based TRL immunoassay for the cardiac troponin I was conducted, exhibiting a limit of detection of 48 pg/mL. On the basis of the features of the LESNP such as TRL signaling capability, stability, and the ease of biofunctionalization, we expect that the LESNP can be widely applied in the development of TRL-based immunosensing.

Multimode smartphone biosensing: the transmission, reflection, and intensity spectral (TRI)-analyzer

We demonstrate a smartphone-integrated handheld detection instrument capable of utilizing the internal rear-facing camera as a high-resolution spectrometer for measuring the colorimetric absorption spectrum, fluorescence emission spectrum, and resonant reflection spectrum from a microfluidic cartridge inserted into the measurement light path. Under user selection, the instrument gathers light from either the white "flash" LED of the smartphone or an integrated green laser diode to direct illumination into a liquid test sample or onto a photonic crystal biosensor. Light emerging from each type of assay is gathered via optical fiber and passed through a diffraction grating placed directly over the smartphone camera to generate spectra from the assay when an image is collected. Each sensing modality is associated with a unique configuration of a microfluidic "stick" containing a linear array of liquid chambers that are swiped through the instrument while the smartphone captures video and the software automatically selects spectra representative of each compartment. The system is demonstrated for representative assays in the field of point-of-care (POC) maternal and infant health: an ELISA assay for the fetal fibronectin protein used as an indicator for pre-term birth and a fluorescent assay for phenylalanine as an indicator for phenylketonuria. In each case, the TRI-analyzer is capable of achieving limits of detection that are comparable to those obtained for the same assay measured with a conventional laboratory microplate reader, demonstrating the flexibility of the system to serve as a platform for rapid, simple translation of existing commercially available biosensing assays to a POC setting.

Overview of the optical properties of fluorescent nanoparticles for optical imaging

Nanoparticles (NPs) include a wide group of small structures composed by very different materials and characterized by peculiar properties that make them suitable for many applications, especially imaging and drug delivery. In this overview, we focus on the optical properties of fluorescent NPs available for in vivo, in vitro and ex vivo preclinical studies and detectable with the optical imaging technique alone or in combination with microscopic confocal imaging. We summarize here the basic principles of the optical detection of fluorescent NPs, elucidating which are the current issues to be resolved and possible solutions to achieve the highest sensitivity and specificity for an unbiased analysis. So far NPs application in clinic is in evaluation due to safety questions still unaddressed but in the future they could dramatically improve both preclinical research and patient clinical care.

Recent advancements in lateral flow immunoassays: A journey for toxin detection in food

Biotechnology embraces various physical and chemical phenomena toward advancement of health diagnostics. Toward such advancement, detection of toxins plays an important role. Toxins produce severe health impacts on consumption with high mortality associated in acute cases. The most prominent route of infection and intoxication is through food matrices. Therefore, rapid detection of toxins at low concentrations is the need of modern diagnostics. Lateral flow immunoassays are one of the emergent and popularly used rapid detection technology developed for detecting various kinds of analytes. This review thus focuses on recent advancements in lateral flow immunoassays for detecting different toxins in agricultural food. Appropriate emphasis was given on how the labels, recognition elements, or detection strategy has laid an impact on improvement in immunochromatographic assays for toxins. The paper also discusses the gradual change in sensitivities and specificities of assays in accordance with the method of food processing used. The review concludes with the major challenges faced by this technology and provides an outlook and insight of ideas to improve it in the future.

Antibody Engineering for Pursuing a Healthier Future

Since the development of antibody-production techniques, a number of immunoglobulins have been developed on a large scale using conventional methods. Hybridoma technology opened a new horizon in the production of antibodies against target antigens of infectious pathogens, malignant diseases including autoimmune disorders, and numerous potent toxins. However, these clinical humanized or chimeric murine antibodies have several limitations and complexities. Therefore, to overcome these difficulties, recent advances in genetic engineering techniques and phage display technique have allowed the production of highly specific recombinant antibodies. These engineered antibodies have been constructed in the hunt for novel therapeutic drugs equipped with enhanced immunoprotective abilities, such as engaging immune effector functions, effective development of fusion proteins, efficient tumor and tissue penetration, and high-affinity antibodies directed against conserved targets. Advanced antibody engineering techniques have extensive applications in the fields of immunology, biotechnology, diagnostics, and therapeutic medicines. However, there is limited knowledge regarding dynamic antibody development approaches. Therefore, this review extends beyond our understanding of conventional polyclonal and monoclonal antibodies. Furthermore, recent advances in antibody engineering techniques together with antibody fragments, display technologies, immunomodulation, and broad applications of antibodies are discussed to enhance innovative antibody production in pursuit of a healthier future for humans.

Microfluidic Surface Plasmon Resonance Sensors: From Principles to Point-of-Care Applications

Surface plasmon resonance (SPR) is a label-free, highly-sensitive, and real-time sensing technique. Conventional SPR sensors, which involve a planar thin gold film, have been widely exploited in biosensing; various miniaturized formats have been devised for portability purposes. Another type of SPR sensor which utilizes localized SPR (LSPR), is based on metal nanostructures with surface plasmon modes at the structural interface. The resonance condition is sensitive to the refractive index change of the local medium. The principles of these two types of SPR sensors are reviewed and their integration with microfluidic platforms is described. Further applications of microfluidic SPR sensors to point-of-care (POC) diagnostics are discussed.

Streptavidin conjugation and quantification-a method evaluation for nanoparticles

Aiming at the development of validated protocols for protein conjugation of nanomaterials and the determination of protein labeling densities, we systematically assessed the conjugation of the model protein streptavidin (SAv) to 100-, 500-, and 1000-nm-sized polystyrene and silica nanoparticles and dye-encoded polymer particles with two established conjugation chemistries, based upon achievable coupling efficiencies and labeling densities. Bioconjugation reactions compared included EDC/sulfo NHS ester chemistry for direct binding of the SAv to carboxyl groups at the particle surface and maleimide-thiol chemistry in conjunction with heterobifunctional PEG linkers and aminated nanoparticles (NPs). Quantification of the total and functional amounts of SAv on these nanomaterials and unreacted SAv in solution was performed with the BCA assay and the biotin-FITC (BF) titration, relying on different signal generation principles, which are thus prone to different interferences. Our results revealed a clear influence of the conjugation chemistry on the amount of NP crosslinking, yet under optimized reaction conditions, EDC/sulfo NHS ester chemistry and the attachment via heterobifunctional PEG linkers led to comparably efficient SAv coupling and good labeling densities. Particle size can obviously affect protein labeling densities and particularly protein functionality, especially for larger particles. For unstained nanoparticles, direct bioconjugation seems to be the most efficient strategy, whereas for dye-encoded nanoparticles, PEG linkers are to be favored for the prevention of dye-protein interactions which can affect protein functionality specifically in the case of direct SAv binding. Moreover, an influence of particle size on achievable protein labeling densities and protein functionality could be demonstrated.

Stem Cell Tracking with Nanoparticles for Regenerative Medicine Purposes: An Overview

Accurate and noninvasive stem cell tracking is one of the most important needs in regenerative medicine to determine both stem cell destinations and final differentiation fates, thus allowing a more detailed picture of the mechanisms involved in these therapies. Given the great importance and advances in the field of nanotechnology for stem cell imaging, currently, several nanoparticles have become standardized products and have been undergoing fast commercialization. This review has been intended to summarize the current use of different engineered nanoparticles in stem cell tracking for regenerative medicine purposes, in particular by detailing their main features and exploring their biosafety aspects, the first step for clinical application. Moreover, this review has summarized the advantages and applications of stem cell tracking with nanoparticles in experimental and preclinical studies and investigated present limitations for their employment in the clinical setting.

Multifunctional quantum dots-based cancer diagnostics and stem cell therapeutics for regenerative medicine

A field of recent diagnostics and therapeutics has been advanced with quantum dots (QDs). QDs have developed into new formats of biomolecular sensing to push the limits of detection in biology and medicine. QDs can be also utilized as bio-probes or labels for biological imaging of living cells and tissues. More recently, QDs has been demonstrated to construct a multifunctional nanoplatform, where the QDs serve not only as an imaging agent, but also a nanoscaffold for diagnostic and therapeutic modalities. This review highlights the promising applications of multi-functionalized QDs as advanced nanosensors for diagnosing cancer and as innovative fluorescence probes for in vitro or in vivo stem cell imaging in regenerative medicine.

Lanthanide-doped luminescent nano-bioprobes for the detection of tumor markers

Sensitive and specific biodetection of tumor markers is essential for early-stage cancer diagnosis and therapy, and will ultimately increase the patient survival rate. As a new generation of luminescent bioprobes, lanthanide (Ln(3+))-doped inorganic luminescent nanoparticles have attracted considerable interest for a variety of biomedical applications due to their superior physicochemical properties. In this feature article, we provide a brief overview of the most recent advances in the development of Ln(3+)-doped luminescent nano-bioprobes and their promising applications for in vitro detection of tumor markers with an emphasis on the establishment of state-of-the-art assay techniques, such as heterogeneous time-resolved (TR) luminescent bioassay, dissolution-enhanced luminescent bioassay, upconversion (UC) luminescent bioassay, homogeneous TR Förster resonance energy transfer (TR-FRET) and UC-FRET bioassays. Some future prospects and efforts towards this emerging field are also envisioned.

Coherent modulation of two-photon up-conversion from colloidal quantum dots by femtosecond laser

The coherent modulation of up-conversion PL of colloidal quantum dots by femtosecond laser has been experimentally and theoretically achieved, which proves that the fs pulse shaping technique can provide an effective method to control two-photon PL.

Controlled morphology and EDTA-induced pure green upconversion luminescence of Er3+/Ho3+-Yb3+ co-doped NaCe(MoO4)2 phosphor

An innovative route to increase the green UC emission and simultaneously suppress red UC emission in Er³⁺/Ho³⁺-Yb³⁺ co-doped NaCe(MoO₄)₂.

Time-resolved luminescent biosensing based on inorganic lanthanide-doped nanoprobes

In this feature article, we review the latest advancements in lanthanide-doped luminescent nanocrystals as time-resolved luminescent nano-bioprobes, from their fundamental optical properties to their potential applications for ultrasensitive biodetection and high-resolution bioimaging.

Ultrasensitive and quantitative gold nanoparticle-based immunochromatographic assay for detection of ochratoxin A in agro-products

In most cases of mycotoxin detection, quantitation is critical while immunochromatographic strip tests are qualitative in nature. Moreover, the sensitivity of this technique is questioned. In order to overcome these limitations, an ultrasensitive and quantitative immunochromatographic assay (ICA) for rapid and sensitive quantitation of ochratoxin A (OTA) was developed. The assay was based on a competitive format and its sensitivity was improved by using a sensitive and selective OTA monoclonal antibody (OTA-mAb). The visible ICA results were obtained within 15 min, and in addition to visual examination, they were read by the rapid color intensity portable strip reader. The visual and computational detection limits (vLOD and cLOD, respectively) for ochratoxin A were 0.2 and 0.25 ng mL(-1), respectively. These values were lower than those reported by previous studies in a range 5-2500 folds. For validation, contaminated samples including wheat, maize, rice and soybean were assayed by ICA and a standard high performance liquid chromatography (HPLC). The results were in good agreement for both ICA and HPLC methods. The average recoveries of the HPLC were in the range 72-120% while the ICA values were from 76 to 104%, confirming the accuracy and sensitivity of this method.

Highly efficient NIR–NIR upconversion in potassium substituted CaMoO4:Tm3+, Yb3+ phosphor for potential biomedical applications

Highly efficient NIR to NIR upconversion in CaMoO₄:Tm³⁺, Yb³⁺ nanocrystals pumped by less than 1 mW laser was achieved for biomedical applications.

Plasmonic biosensors

The unique optical properties of plasmon resonant nanostructures enable exploration of nanoscale environments using relatively simple optical characterization techniques. For this reason, the field of plasmonics continues to garner the attention of the biosensing community. Biosensors based on propagating surface plasmon resonances (SPRs) in films are the most well-recognized plasmonic biosensors, but there is great potential for the new, developing technologies to surpass the robustness and popularity of film-based SPR sensing. This review surveys the current plasmonic biosensor landscape with emphasis on the basic operating principles of each plasmonic sensing technique and the practical considerations when developing a sensing platform with the various techniques. The 'gold standard' film SPR technique is reviewed briefly, but special emphasis is devoted to the up-and-coming localized surface plasmon resonance and plasmonically coupled sensor technology.