Optical sensing of biomedically important polyionic drugs using nano-sized gold particles

Detection of protamine based on competitive adsorption onto the surface of functionalized multi-walled carbon nanotubes

This study developed an adsorption-based determination system for protamine. A multi-walled carbon nanotube (MWCNT), which is a strong adsorbent, was used. The competitive adsorption process between dyes and protamine formed the basis of the sensor system. The adsorption process was followed over the dyes by UV-Vis. absorption spectroscopy. This sensor system was developed using the thermodynamic parameters. Transmission electron microscopy and Fourier-transform infrared spectroscopy techniques were used for the characterization of the sensor system. It was determined that the sensor system remained stable at physiological temperature and pH range. Limit of detection values of PyB-COO-MWCNT and PyY-COO-MWCNT systems were found to be 1.32 and 1.12 ng mL-1 , respectively. The applicability of the sensor systems was demonstrated using bovine serum solutions.

Determination of protamine and heparin based on their effects on a glucose oxidase enzymatic reaction

This paper describes a sensitive method for determining protamine and heparin by utilizing a glucose oxidase enzymatic reaction. Polycationic protamine significantly promoted the enzymatic reaction rate with [Fe(CN)6]3-, so that the increase could be used to determine protamine. The promotion effect was stoichiometrically decreased by the addition of polyanionic heparin through the polyion complex formation with protamine, so that the enzymatic reaction also allowed for the determination of heparin. We thus applied the proposed method to blood plasma containing heparin and found that heparin did not stoichiometrically form a polyion complex with protamine, likely due to strong interactions between heparin and some components of the plasma. The proposed method allowed for the detection of free protamine (and/or weakly binding protamine with heparin) existing in the condition that protamine did not neutralize all of the heparin in the plasma. The method also permitted for the estimation of heparin concentrations using calibration curves. Thus, the proposed method would help reduce the risks of protamine overdose in heparin neutralization and would be a helpful tool in clinical practices that use heparin and protamine.

Recent advances and perspectives of enzyme-based optical biosensing for organophosphorus pesticides detection

The overuse or abuse of organophosphorus pesticides (OPs) can bring about severe contamination problems in foodstuff and the environment, which will seriously threaten human health and the ecosystem's cycle. Hence, it is in high demand to establish sensitive, portable, specific, and cost-effective methods for monitoring OPs to control food safety, protect the ecosystem, and prevent disease. The optical biosensor with enzyme as bio-recognition elements has been an effective alternative for OPs detection. Herein, we firstly introduce various enzymes, sensing mechanisms, advantages and disadvantages used as bio-recognition elements in optical sensing for OPs detection. Then, we review various optical biosensing strategies based on enzymes as recognition elements that were ingeniously designed and successfully utilized for OPs detection, with a particular emphasis on photoluminescence (PL), chemiluminescence (CL), electrochemiluminescence (ECL), and colorimetric (CM) biosensing strategies. We not only highlight the state-of-art developments and the construction strategies of the enzyme-based optical biosensing method but also summarize the existing deficiencies, current challenges, and the future perspectives of OPs detection.

Designing a two-stage colorimetric sensing strategy based on citrate reduced gold nanoparticles: Sequential detection of Sanguinarine (anticancer drug) and visual sensing of DNA

Distance dependent optical properties of colloidal gold nanoparticles offer designing of colorimetric sensing modalities for detection of a variety of analytes. Herein, we report a simple and facile colorimetric detection assay for an anti-cancer drug, Sanguinarine (SNG) and Calf Thymus DNA (Ct-DNA) based on citrate reduced gold nanoparticles (CI-Au NPs). The electrostatic interaction between SNG and CI-Au NPs induce aggregation of Au NPs accompanied with visible colour change of colloidal solution. The assay conditions like salt concentration, pH and reaction time had been adjusted to achieve highly sensitive and fast colorimetric response. Furthermore, the optimized CI-Au NPs/SNG sensing system is used for the detection of Ct-DNA based on the mechanism of anti-aggregation of CI-Au NPs. The simultaneous presence of SNG and Ct-DNA prevent aggregation of Au NPs owing to preferential formation of Ct-DNA-SNG intercalation complex and colour of the Au NPs solution tends to remain red, depending on the concentration of Ct-DNA in solution. The degree of aggregation and anti-aggregation of CI-Au NPs was monitored using Transmission electron microscopic (TEM) measurements and UV-Visible spectrophotometry by analysing the ratio of absorptions for aggregated and dispersed Au NPs. The intercalation mode of binding between SNG and Ct-DNA in CI-Au NPs/SNG sensing system was determined by Fluorescence spectral studies and UV-thermal melting studies. The absorption ratio (A₆₂₇/A₅₂₅) of Au NPs exhibited a linear correlation with SNG concentrations in the range from 0 to 0.9 μM with detection limit as 0.046 μM. This optical method can determine Ct-DNA as low as 0.36 μM and the calibration is linear for concentration range 0 to 5 μM. The proposed sensing strategy enables detection as well as quantification of SNG & Ct-DNA in real samples with satisfactory results and finds application in drug or DNA monitoring.

An anionic polyelectrolyte induced aggregate assembly of Thioflavin-T: A prospective platform for Protamine sensing

Protamine, a polycation, is biologically and medically relevant protein. Protamine exhibits a wide array of functions in biological processes like gene transfer, tissue and organogenesis, cell reproduction, etc. Medically, Protamine is the only clinically approved antidote for Heparin and is routinely used in various surgical interventions, and hence controlling Protamine dosing in patients is very crucial. Taking into account the medical significance of Protamine, designing simple, reliable and sensitive fluorescence sensors is highly desirable. In this work, we propose one such sensitive and reliable fluorescent sensor which is based on a template of dye-polyelectrolyte assembly constituting a molecular rotor dye, Thioflavin-T and an anionic synthetic polyelectrolyte, polystyrene sulfonate. The addition of Protamine, prompts drastic modulations in spectral features of dye-polyelectrolyte assembly which enables sensitive detection of Protamine in aqueous solution. Apart from sensitive detection, our sensing platform aids in highly selective sensing of Protamine compared to other proteins. Moreover, our sensor system is constructed on label-free, inexpensive, commercially available molecules posing as an advantage over other sensor systems which involve laborious synthesis protocols. Most importantly, our sensor template is able to sense Protamine in diluted serum sample, indicating the potential practical utility of our sensor system.

A heparin-modified palladium nanozyme for photometric determination of protamine

Heparin was employed as the stabilizing agent in the synthesis of peroxidase-mimicking Pd nanoparticles. The heparin-capped Pd nanozyme can act as both the signal amplifier and the selective binder of protamine. The most efficient nanozyme with the mean size of 3.5 nm consists of 70.8% metallic Pd⁰ and 29.2% Pd²⁺ species. Enzyme kinetic studies show that the K_m values are 0.036 mM for 3,3',5,5'-tetramethylbenzidine and 78 mM for H₂O₂. Protamine shows strong affinity to the heparin-capped Pd nanozyme, and induces an apparent aggregation of the nanoparticles. This results in a significant inhibition of the peroxidase-mimicking activities. Hence, the oxidation of TMB by H₂O₂ to a blue product with a maximum absorption at 652 nm is suppressed. Based on this finding, a photometric assay is developed for the determination of protamine. The linear response is in the concentration range 0.02 ~ 0.8 μg mL^-1, and the limit of detection is 0.014 μg mL^-1. This assay presents high selectivity toward other biological substances. Graphical abstract Highly active and selective Pd nanozyme was synthesized through adopting heparin as the capping agent for quantitative determination of protamine.

Ratiometric Fluorescent Quantum Dot-Based Biosensor for Chlorothalonil Detection via an Inner-Filter Effect

A new sensitive sensor for detecting chlorothalonil (CHL) based on the inner-filter effect (IFE) between gold nanoparticles (AuNPs) and ratiometric fluorescent quantum dots (RF-QDs) was developed. Here, RF-QDs were designed by two different color CdTe QDs. Based on the IFE, the AuNPs can quench the fluorescence of the RF-QDs. Because of the electrostatic attraction between protamine (PRO) and the AuNPs, the PRO can restore fluorescence effectively. Papain (PAP) can easily hydrolyze PRO and causes the quench of fluorescence quenching. The addition of CHL can inhibit PAP activity and restore the fluorescent signal. Through the characterization of the structural changes of PAP, the inhibition and mechanism of CHL on PAP activity were studied. The ability of CHL to inhibit PAP activity was evaluated by measuring the fluorescence of the RF-QDs. Under the optimal conditions, this sensing platform shows a response to CHL in the range of 0.34-2320 ng/mL and a detection limit of 0.0017 ng/mL. Based on the CHL inhibition of PAP activity, the RF-QDs showed good selectivity for CHL. The practical application of the proposed system was demonstrated by detecting CHL in food and environmental samples with satisfying results.

A gold–carbon dots nanoprobe for dual mode detection of ketamine HCl in soda drinks

Fluorescent and color sensors for ketamine HCl determination. A dual-mode nanoprobe for the detection of a club drug in spiked beverage.

Fabrication of Orange-Emitting Organic Nanoparticle-Protamine Conjugate: Fluorimetric Sensor of Heparin

Among the diverse sensing techniques, fluorimetric detection dominates over the other methods because of its rapid signaling, high selectivity and sensitivity, and operational simplicity. This present article delineates fabrication of a fluorescent organic nanoparticle-protamine (FONP-Pro) conjugate for selective and sensitive detection of heparin simply by exploitation of the aggregation-induced emission (AIE) property of the FONPs. Naphthalene diimide-based bola-type amphiphilic molecules (NDI-1) comprise a naphthyl residue and a 3-aminopyridyl unit at both terminals, forming organic nanoparticles in a dimethyl sulfoxide-water binary solvent mixture, and exhibited AIE through excimer formation. The presence of naphthyl residue in the molecular backbone facilitates the intramolecular charge transfer to generate orange-emitting (λ_em = 594 nm) AIE-luminogen (AIE-gen). The aminopyridine residues within NDI-1 induced negative surface charge on NDI-1 FONPs, which facilitated interaction with positively charged protamine (Pro) to construct FONP-Pro conjugates. Formation of this NDI-1 FONP-Pro conjugate through the interaction between Pro and FONP drastically reduced the orange emission intensity (fluorescence off) of the AIE-gens. Interestingly, addition of heparin to this FONP-Pro conjugate turned on the fluorescence signal of FONPs through unwinding of the Pro from the FONP surface because of a strong binding affinity between heparin and Pro. Formation of the FONP-Pro conjugate and fluorimetric sensing of heparin was investigated by monitoring the change in emission behavior of NDI-1 FONPs. Also, the heparin-sensing was found to be highly selective against many other biomolecules including proteins, enzymes, and DNA. Hence, a selective and efficient heparin sensor (FONP-Pro) was developed having a limit of detection of 12 nM simply by utilizing the fluorescence "turn-off" and "turn-on" mechanism of NDI-1 FONP.

Aggregation-Induced Emission Enhancement of CdSe QDs by Protamine and its Application to Sensitively and Selectively Detect Heparin

Background:

Heparin, it is commercially used as an anticoagulant in surgical procedures for the prevention of blood clotting. However, overdose and prolonged use of heparin often induce potentially fatal bleeding complication. So, it is of crucial importance to monitor closely heparin levels for the sake of health. In this work, a sensitive fluorescence sensing platform to detect heparin was set up based on MPA-CdSe QDs (quantum dots) and protamine enhanced fluorescent system.

Methods:

The image of CdSe QDs was taken on a JEM-2100 transmission electron microscope (JEOL Ltd.). The fluorescence spectrum was recorded on a FluoroMax-4 fluorescence spectrophotometer (Horiba, USA). UV–vis absorption spectrum was recorded using a Shimadzu UV-2450 Spectrophotometer (Tokyo, Japan). A vortex mixer IKA MS3 digital was selected to mix the solution.

Results:

Under optimized conditions, the linear response to detect heparin ranges from 0.06 to 14 µg mL-1 with a detection limit of 8 ng mL-1. The approach showed a highly selective response to heparin in the presence of 16 interfered substances.

Conclusion:

A simple method for the detection of heparin was developed based on MPA-CdSe QDs and protamine enhanced fluorescent system. The electrostatic effect between MPA-CdSe QDs and protamine resulted in strong fluorescence enhancement from the MPA-CdSe QDs. Moreover, the addition of heparin could cause a significant fluorescence decrease due to the strong affinity of protamine and heparin. Under optimal conditions, this method displayed a low detection limit and good selectivity over other substances.

Reversible fluorescence modulation of BSA stabilised copper nanoclusters for the selective detection of protamine and heparin

Depicting fluorescence sensing of protamine and heparin based on aggregation and disaggregation of copper nanoclusters.

A fluorometric sensing method for sensitive detection of trypsin and its inhibitor based on gold nanoclusters and gold nanoparticles

In this work, a facile, label-free, and sensitive fluorometric strategy for detection of trypsin and its inhibitor was established on the basis of the fluorescence resonance energy transfer (FRET) between mercaptoundecanoic acid functionalized gold nanoclusters (AuNCs) and gold nanoparticles (AuNPs) via protamine as a bridge. Protamine can trigger the aggregation of AuNPs and link AuNCs with aggregated AuNPs through electrostatic interaction. Compared with monodisperse AuNPs, the UV-vis absorption band of aggregated AuNPs overlapped considerably with the emission spectrum of AuNCs. Thus, the fluorescence of AuNCs was obviously quenched by the aggregated AuNPs through FRET. In the presence of trypsin, protamine was hydrolyzed into small fragments, leading to the deaggregation of AuNPs and breaking of the short distance between AuNPs and AuNCs, so the FRET process was inhibited, and the fluorescence of AuNCs was recovered. The increase in the fluorescence intensity of AuNCs was directly related to the amount of trypsin. Hence trypsin can be determined on the basis of the variation of fluorescence intensity, with a linear range of 5-5000 ng mL-1 and a detection limit of 1.9 ng mL-1. In addition, this system was used for the detection of trypsin inhibitor by application of the inhibitor isolated from soybean as a model. The sensing method was applied for trypsin detection in human urine and commercial multienzyme tablet samples with satisfactory results. Graphical abstract ᅟ.

Fluorescent Strips of Electrospun Fibers for Ratiometric Sensing of Serum Heparin and Urine Trypsin

"Turn-on" or "turn-off" probes remain challenges in the establishment of sensitive, easily operated, and reliable methods for in situ monitoring bioactive substances. In the current study, electrospun fibrous strips are designed to provide straightforward observations of ratiometric color changes with the naked eye in the presence of serum heparin or urine trypsin. A tetraphenylethene (TPE) derivative is constructed and along with phloxine B is grafted on fibers, followed by protamine adsorption to induce static quenching of phloxine B and aggregation-induced emission of the TPE derivative. The presence of heparin or trypsin removes protamine to restore the fluorescence of phloxine B at 574 nm (I₅₇₄) and relieve the emission of the TPE derivative at 472 nm (I₄₇₂). The grafting densities of phloxine B and the TPE derivative are essential to achieve the optimal fluorescence-intensity ratio of I₅₇₄/I₄₇₂ for the ratiometric detection of heparin and trypsin. Under illumination by an ultraviolet lamp, the fibrous mats turn from cyan to green in the presence of heparin at 0.4 U/mL and to a bright yellow at 0.8 U/mL, which is feasible in sensing serum heparin levels during postoperative and long-term care of patients after cardiovascular surgery. The protamine digestion results in similar color transitions with increasing trypsin levels up to 8 μg/mL, indicating the potential for monitoring urine trypsin levels of pancreas transplant patients. The color strips based on the ratiometric fluorescent response indicate advantages in lowering the detection limit and improving the accuracy and reproducibility, bearing great potential for a real-time and naked-eye detection of bioactive substances as self-test devices.

Optical probes and sensors as perspective tools in epigenetics

Modifications of DNA cytosine bases and histone posttranslational modifications play key roles in the control of gene expression and specification of cell states. Such modifications affect many important biological processes and changes to these important regulation mechanisms can initiate or significantly contribute to the development of many serious pathological states. Therefore, recognition and determination of chromatin modifications is an important goal in basic and clinical research. Two of the most promising tools for this purpose are optical probes and sensors, especially colourimetric and fluorescence devices. The use of optical probes and sensors is simple, without highly expensive instrumentation, and with excellent sensitivity and specificity for target structural motifs. Accordingly, the application of various probes and sensors in the recognition and determination of cytosine modifications and structure of histones and histone posttranslational modifications, are discussed in detail in this review.

A pyrene-based fluorescent sensor for ratiometric detection of heparin and its complex with heparin for reversed ratiometric detection of protamine in aqueous solution

An imidazolium-modified pyrene derivative, IPy, was used for ratiometric detection of heparin, and its complex with heparin was used for reversed ratiometric detection of protamine in both aqueous solution and serum samples. The cationic fluorescent probe could interact with anionic heparin via electrostatic interaction to bring about blue-to-green fluorescence changes as monomer emission significantly decreases and excimer increases. The binary combination of IPy and heparin could be further used for green-to-blue detection of protamine since heparin prefers to bind to protamine instead of the probe due to its stronger affinity with protamine. The cationic probe shows high sensitivity to heparin with a low detection limit of 8.5nM (153ng/mL) and its combination with heparin displays high sensitivity to protamine with a detection limit as low as 15.4nM (107.8ng/mL) according to the 3σ IUPAC criteria. Moreover, both sensing processes are fast and can be performed in serum solutions, indicating possibility for practical applications.

Fluorescence sensor for detecting protamines based on competitive interactions of polyacrylic acid modified with sodium 4-amino-1-naphthalenesulfonate with protamines and aminated graphene oxide

An easy-to-use fluorescent probe for detecting protamines was developed.

A luminescent and colorimetric probe based on the functionalization of gold nanoparticles by ruthenium(ii) complexes for heparin detection

A colorimetric and luminescent bifunctional Ru(ii) complex-modified gold nanoprobe for the sensing of heparin in Tris-HCl buffer (pH 7.4) and 1% fetal bovine serum (FBS) was developed.

Colorimetric detection based on localised surface plasmon resonance of gold nanoparticles: Merits, inherent shortcomings and future prospects

Localised surface plasmon resonance (LSPR) of gold nanoparticles (AuNPs) has been exploited for two decades in analytical science and has proven to be a powerful tool for the detection of various kinds of substances including small molecules, ions, macro biomolecules and microbes. Detection can be performed by visual colour change observations, photometry or resonance light scattering. A wide range of applications have been studied in the areas of environmental, pharmaceutical and biological analysis and clinical diagnosis. In this article, some fundamental aspects and important applications involving LSPR of AuNPs are reviewed. Several inherent shortcomings of these techniques and possible strategies to circumvent them are discussed.

Studies on the interaction of heparin with lysozyme by multi-spectroscopic techniques and atomic force microscopy

The interaction between heparin (Hep) and lysozyme (Lyso) in vitro was studied by fluorescence, UV-vis, circular dichroism (CD), resonance Rayleigh scattering (RRS) spectroscopy and atomic force microscopy (AFM) under normal physiological conditions. UV-vis spectra of Lyso showed the absorbance was significantly increased with the addition of Hep. Fluorescence studies revealed that the emission quenching of Lyso with Hep was initiated by static quenching mechanism. CD spectral studies showed that Hep induced conformational changes in the secondary structure of Lyso. RRS spectra of Lyso showed the intensity of scattering was significantly increased with the addition of Hep and the enhanced RRS intensities were proportional to the concentration of Hep in a certain range. Thus, a new RRS method using Lyso as a probe could be used for the determination of Hep. The detection limit for Hep was 3.9 ng mL(-1). In addition, the shape of the complex was characterized by AFM. The possible reaction mechanism and the reasons for the enhancement of RRS intensity had been discussed through experimental results.

Aggregation of layered double hydroxide nanoparticles in the presence of heparin: towards highly stable delivery systems

Heparin coating significantly enhanced the colloidal stability of layered double hydroxide nanoparticles.

A ratiometric fluorescent quantum dots based biosensor for organophosphorus pesticides detection by inner-filter effect

In this work, we develop a novel and sensitive sensor for the detection of organophosphorus pesticides based on the inner-filter effect (IFE) between gold nanoparticles (AuNPs) and ratiometric fluorescent quantum dots (RF-QDs). The RF-QDs has been designed by hybridizing two differently colored CdTe QDs, in which the red emissive QDs entrapped in the silica sphere acting as the reference signal, and the green emissive QDs covalently attached on the silica surface serving as the response signal.The fluorescence of RF-QDs could be quenched by AuNPs based on IFE. Protamine could effectively turn on the fluorescence due to the electrostatic attraction between protamine and AuNPs. Trypsin can easily hydrolyze protamine, leading to the quench of the fluorescence. Then, the fluorescence could be recovered again by the addition of parathion-methyl (PM) which could inhibit the activity of trypsin. By measuring the fluorescence of RF-QDs, the inhibition efficiency of PM to trypsin activity was evaluated. Under the optimized conditions, the inhibition efficiency was proportional to the logarithm of PM concentration in the range of 0.04-400 ng mL(-1), with a detection limit of 0.018 ng mL(-1). Furthermore, the simple and convenient method had been used for PM detection in environmental and agricultural samples with satisfactory results.

A simple and rapid label-free fluorimetric biosensor for protamine detection based on glutathione-capped CdTe quantum dots aggregation

A novel fluorescent biosensor is developed, based on glutathione-capped CdTe quantum dots aggregation, for the determination of trace amount of an important drug, protamine. In this method with increasing the protamine concentration, the fluorescence of the quantum dots was quenched due to their aggregation. Different parameters affect the sensitivity, such as pH and the amount of the quantum dots, were optimized. Using the new optical biosensor, under the optimized conditions, protamine could be measured in the range of 2.0-200 ng mL(-1) with a detection limit of 1.0 ng mL(-)(1). The relative standard deviation for five replicates determination of 30.0 ng mL(-)(1) protamine was 1.26%. The influence of common interfering species on the protamine detection was studied. The results showed that the biosensor is highly selective and sensitive for the detection of protamine. The optical biosensor was successfully used for the determination of protamine in real samples.

Nanomaterials based electrochemical sensors for biomedical applications

A growing variety of sensors have increasingly significant impacts on everyday life. Key issues to take into consideration toward the integration of biosensing platforms include the demand for minimal costs and the potential for real time monitoring, particularly for point-of-care applications where simplicity must also be considered. In light of these developmental factors, electrochemical approaches are the most promising candidate technologies due to their simplicity, high sensitivity and specificity. The primary focus of this review is to highlight the utility of nanomaterials, which are currently being studied for in vivo and in vitro medical applications as robust and tunable diagnostic and therapeutic platforms. Highly sensitive and precise nanomaterials based biosensors have opened up the possibility of creating novel technologies for the early-stage detection and diagnosis of disease related biomarkers. The attractive properties of nanomaterials have paved the way for the fabrication of a wide range of electrochemical sensors that exhibit improved analytical capacities. This review aims to provide insights into nanomaterials based electrochemical sensors and to illustrate their benefits in various key biomedical applications. This emerging discipline, at the interface of chemistry and the life sciences, offers a broad palette of opportunities for researchers with interests that encompass nanomaterials synthesis, supramolecular chemistry, controllable drug delivery and targeted theranostics in biology and medicine.

Highly sensitive surface-enhanced Raman scattering sensing of heparin based on antiaggregation of functionalized silver nanoparticles

We report a simple and sensitive surface-enhanced Raman scattering (SERS) platform for the detection of heparin, based on antiaggregation of 4-mercaptopyridine (4-MPY) functionalized silver nanoparticles (Ag NPs). Here, protamine was employed as a medium for inducing the aggregation of negatively charged 4-MPY functionalized Ag NPs through surface electrostatic interaction, which resulted in significantly enhanced Raman signal of the Raman reporter. However, in the presence of heparin, the interaction between heparin and protamine decreased the concentration of free protamine, which dissipated the aggregated 4-MPY functionalized Ag NPs and thus decreased Raman enhancement effect. The degree of aggregation and Raman enhancement effect was proportional to the concentration of added heparin. Under optimized assay conditions, good linear relationship was obtained over the range of 0.5-150 ng/mL (R(2) = 0.998) with a minimum detectable concentration of 0.5 ng/mL in standard aqueous solution. Furthermore, the developed method was also successfully applied for detecting heparin in fetal bovine serum samples with a linear range of 1-400 ng/mL.

Investigation of Luminescence Characteristics of Osmium(II) Complexes in the Presence of Heparin Polyanions

The luminescence characteristics of six osmium carbonyl complexes with phenanthroline (phen) or bipyridine (bpy) and pyridine (py), 4-phenylpyridine (4-phpy), or triphenylphosphine (PPh3) complexes in the presence of polyanion heparin were studied in both ethanol and aqueous solutions. The influence of heparin on the luminescence of the complexes is heavily dependent on the type of ligands in the complexes and the solvent used. In the ethanol solutions, the heparin solution enhanced the luminescence of the five osmium complexes, with the strongest enhancement to the 4-phenylpyridine complexes; linear curves were obtained in the luminescence enhancement ratio (F/F 0) versus the heparin concentration range of 1-40  μ g/mL. In aqueous solutions, heparin quenching of the complexes was more significant; a linear quenching curve was obtained with [Os(phen)2CO(PPh3)](PF6)2 in the lower concentration range of 1-12  μ g/mL. The interaction of these complexes with heparin in the solutions is discussed. The complexes are shown to be successful in the fast and sensitive detection of heparin in commercial injectable samples.

Ultrasensitive surface-enhanced Raman scattering detection of trypsin based on anti-aggregation of 4-mercaptopyridine-functionalized silver nanoparticles: an optical sensing platform toward proteases

In this work, a simple and sensitive surface-enhanced Raman scattering (SERS) strategy was developed for recognition and detection of trypsin, by using anti-aggregation of 4-mercaptopyridine (4-MPY)-functionalized silver nanoparticles (AgNPs) based on the interaction between protamine and trypsin. The polycationic protamine not only served as a substrate for enzyme hydrolysis but also worked as a medium for SERS enhancement, which could bind negatively charged 4-MPY-functionalized AgNPs and induce their aggregation. The hydrolysis catalyzed with trypsin in sample solution decreased the concentration of free protamine, resulting in the dispersion of AgNPs and thus decreasing the Raman intensity of 4-MPY, by which the trypsin could be sensed optically. A detection level down to 0.1 ng mL(-1) for trypsin was obtained. The induced accumulation of AgNPs modified with Raman reporter 4-MPY largely enhanced the SERS responses. A good linearity was found within the wide range over five orders of magnitude and reasonable relative standard deviations (between 2.4 and 11.6%) were attained. By using trypsin as a model, the new concept can provide an excellent platform for ultrasensitive SERS measurements of various proteases/enzymes which can lead to nanoparticles stability change through catalyzed hydrolysis toward substrate.

Remotely Triggered Drug Release from Gold Nanoparticle-based Systems

Nanoparticles are attractive drug carriers that can combine drug molecules and targeting moieties in order to improve treatment efficacy and reduce unwanted side effects. In addition, activatable nanoparticles may enable drug release in the target sites at accurate timings or conditions, in which drug discharge can be controlled by specific stimuli. Especially, gold nanoparticles provide a great opportunity as drug carriers because of the following advantageous features: i) simple formulation with various sizes and shapes and non-toxicity; ii) easy incorporation of targeting molecules, drugs or other therapeutic molecules on them; iii) triggered drug release by means of external or internal stimuli. In this chapter, we describe relevant examples of the preparation techniques and the performance of various types of gold nanoparticles for drug delivery as well as theranostics.