The steady growth of the global market for dyes and pigments indicates a bright future for research in the corresponding broad research field. In fact, the majority of the currently known classes of dyes and pigments were invented during the 19th century.
Results and discussion
- The bisensing solvatochromic compounds 1 and 2a,b
- Resonance structures of compounds 1 and 2a,b
- Solute-solvent interactions
- Quantification of the solvatochromism of the FC and azo groups
- Single solvent polarity parameter involving LSERs
- Multiprameteric LSERs
- PS effects as sensed by the FC and azo groups
Here the author reports relevant results concerning the solvatochromism of the azo group (n!π∗ transitions). 8 and 9 (contribution analysis), the relative contribution of each of the parameters π*, α, and β was quantified (detailed results in Table 3).
Conclusions
A study of preferential solvation in a mixed binary solvent as a function of solvent composition and temperature by UV-vis spectroscopic method. A study of preferential solvation effects in binary solvent mixtures using intensely solvatochromic azobenzene involving [2]rotaxane solutes.
Introduction
Research and evaluation of dyes play a crucial role in the process of introducing new labels and their associated detection methods, which offer opportunities for the development of biosensors. The dyes used in this field have been summarized and rated according to their signal types, namely colorimetric, fluorescent and electrochemical. Due to the rapid development of nanotechnology and materials science, nanomaterials are widely accepted as biosensing labels, many of which are dyes in the sense of optics or electrochemistry.
The special size of these nanomaterial dyes offers unique properties that significantly improve the performance of relevant biosensors. In this chapter, we focus on dyes used as biosensing labels and discuss their properties, applications, and how they enhance biosensing properties.
Dyes in colorimetric biosensors
Gold nanoparticles
Several GNP-based colorimetric biosensors were built, relying on the same principle, namely surface plasmon resonance (SPR). Based on the SPR effect, GNPs have also been used in other types of biosensors, for example surface-enhanced Raman spectroscopy (SERS) based sensing. The most well-known biosensing application of GNPs must be the pregnancy test sticks, which belong to the most commercialized type of biosensor, i.e. the lateral flow (LF) system.
Since then, a new generation of medical diagnostic technology based on the nanomaterials has begun. Oligonucleotides, peptides, antibodies, and aptamers have been labeled with GNPs for colorimetric detection of various targets based on the similar principle.
Carbon nanoparticles
Such strategy designs usually achieve nanomolar detection limits, which are limited by the signal-to-noise ratio related to the intrinsic properties of labels and sensors [ 22 ]. In order to amplify the signals and optimize the performance of the biosensor, the biochemical and molecular amplification methods are introduced in the biosensing process. Via duplex-specific nuclease-assisted amplification method, a colorimetric method for microRNA detection based on GNPs aggregation was developed [23].
DNAzyme-assisted target recycling was used, combined with surface plasmons of GNP linkage in the colorimetric biosensor, providing fast and easy detection of genetic targets with a sensitivity of 50 pM [24]. Using imaging-based analysis instead of spectrographic analysis has a higher signal-to-noise ratio and thus potentially a lower limit of detection.
Latex particles
A dark-field microscope-based methodology was applied for the observation of GNP aggregation, obtaining a detection limit of 43 aM DNA, which was 5–9 orders of magnitude lower than conventional colorimetric sensor-based strategies [ 25 ]. There are three ways to prepare colored latex particles by dyeing latex particles with different types of dye molecules: (1) co-polymerization of polymer monomer with dyes; (2) cross-linking of the dyes on particles' surface by covalent bonds; (3) physical embedding or absorption of dyes into particles. Benefiting from the wide variety of sources, low cost and easy to functionalize, the latex particles are early employed as probes in immunochromatographic analysis [29].
A lateral flow immunoassay was developed by covalently functionalizing the antigens on colored latex particles for the visual diagnosis of visceral leishmaniasis in dogs [30]. A latex particle-GNPs composite labeled with antibodies was synthesized as tested for the immunochromatographic assay.
Dyes in fluorescent biosensors
Organic dyes
However, when they are embedded in specific DNA structures, the fluorescence intensity will increase significantly, due to the protection of the hydrophobic groups of the oligonucleotide (Figure 5). Due to the length and/or the secondary structure of the oligonucleotide, the probe holds the fluorophore and quencher close together, thus causing a quench. Therefore, the fluorescence emission intensity of the original monomer weakens or disappears, and the fluorescence emission of the formed excimer appears [ 42 , 43 ].
The doubly labeled probes are all distance dependent, the rearrangement of the probe structure after binding to the target molecules will change the distance between the two labels, resulting in changes in the fluorescence properties of the system. Compared with covalently binding fluorescent probes, the non-covalently binding fluorescent probes will not affect the binding affinity of the probe to the target, and they also have the advantages of easy operation and low cost [ 47 ].
Quantum dots
Due to the tunable size and wide spectral width, QDs can play as energy donors or acceptors in the FRET biosensor [72]. QDs can be easily used as fluorescent labels in immunosensors to quantify the biological targets by directly measuring the presence and/or intensity of the fluorescence. Direct binding: Proteins and nucleic acids can be immobilized directly on the QD surface through interactions between the thiol groups or imidazole groups with the metal component of QDs, e.g. DNAs with alkylthiol end groups are linked directly to the QD surface via dative thiol binding [79].
Conjugation via ligands: QDs can be first functionalized by ligands, such as carboxyl groups, hydroxyl groups, and amino groups, and then covalently attached to biomolecules [80]. Conjugation via specific biological affinity: some types of biological affinity can be used to bind the QDs with biomolecules strongly and specifically, such as biotin-streptavidin interaction [83].
Upconversion fluorescent materials
Dyes in electrochemical biosensors
Organic dye molecules
Organometallic complexes
Since Fc has two freely rotating cyclopentadiene rings, it can be labeled with the biomolecules, such as DNA, through hydrophobic interactions. As an electrical signal molecule, in the combination of bioreceptors and target molecules, Fc generates electrical signals mainly by adjusting the distance between the Fc and the electrode surface to realize the change of electrical signal and achieve the purpose of detection. They are mainly used as electron transfer agents in amperometric biosensors, to replace the natural electron transfer agents of the enzymes.
In commercial blood glucose meters, blood glucose reacts with glucose oxidase and K3[Fe(CN)6] immobilized on the surface of the test strip to produce gluconic acid and K4[Fe(CN)6].
Nanomaterials .1 Quantum dots
However, although MOFs have enzymatic activity to improve sensitivity, their synthesis process is very complicated, and the characterization of the modification process is also very critical, so they are not suitable for routine use.
Conclusion
This article discusses the role of natural dyes, from coloring the cotton fabrics with some functionality to harvesting sunlight into the dye-sensitive solar cells. Electrochemical research to explore the potential of natural dyes as a sensitizer will be discussed, for example natural dyes for Batik. The advantage of using natural dyes lies in the smoothness and softness of the color.
Natural dyes that, in addition to indigo blue, are currently widely used for batik production are Tingi (Ceriops tagal) natural dyes. Finally, some ideas for improving solar cell performance with natural dyes will be presented in the concluding remarks.
Improving the wash-fastness of the natural dyed cotton fabrics
The wash fastness of the dyed material was tested by immersing the test samples in 1% SDS (sodium dodecyl sulfate) solution (in water) at room temperature. Compared with cotton cloth without the addition of silica nanosol, the mixture composition of silica nanosol dye can increase the wash fastness resistance of the dye over the washing process. Just recently, similar effect can also be obtained by using chitosan coating on the dyed cotton [9].
It is anticipated that the chitosan structure may provide more functional groups for hydrogen bonding with either cellulose from the cotton fabrics or the dye (represented by procyanidin as the active dye of the Tingi extract). Therefore, the mixture of chitosan and dye solutions resulted in lower leaching rates for SDS than for the dye itself.
Hydrophobic surfaces on natural dyed cotton fabrics
Figures 5 and 6 showed the reflectance spectra to confirm the effect of silica nanosol on mixing colored sols. The leaching rate of up to 6.24% has been achieved for the dyeing process using a mixture of chitosan and Tingi extract [9]. The nanosol blend coated fabric showed the best hydrophobicity properties with the largest water contact angle value of 134.7°, while the layer by layer coated fabric gave the lowest hydrophobicity.
Our recent results for chitosan coating mixture have shown improved water contact angle after leaching test with natural detergent (Sapindus rarak). A ten percent improvement was achieved for the fabrics dyed with a mixture of chitosan-Tingiextract dye, resulting in a water contact angle of
Natural dyes for dye-sensitized solar cells: Batik and Algae ’ s extract A dye-sensitized solar cell (DSSC) is one promising alternative to conventional
The HOMO energy level of the dyes was then calculated from the onset of the anodic potential of the cyclic voltammograms. The solar cell's order of efficiency corresponds to the ease of electron injection of the dyes into the conduction band of TiO2. The width of the TiO2 band gap reflects the nature of the photostability due to the electron recombination.
These studies encourage the use of 1D nanostructured TiO2 to improve the performance of natural dye solar cells. The intrinsic properties of natural dyes that have rich antioxidants are providing the potential for multifunctional antibacterial textiles.
Concluding remarks
Synthesis and characterization of three organic dyes with different donors and rhodamine ring acceptor for use in dye-sensitized solar cells. Robust organic dye for dye-sensitized solar cells based on iodine/iodide electrolytes combines high efficiency and. Optimizing a simple method for natural dye preparation for dye-sensitized solar cells: Examples of Betalain (bougainvillea and beetroot extracts) and anthocyanin dyes.
Solvothermal growth of well-aligned TiO2nanowire arrays for dye-sensitized solar cell: dependence of morphology and vertical orientation on substrate pretreatment. Efficient way to improve the efficiency of a quasi-solid state dye-sensitized solar cell by harvesting the unused higher energy visible light using carbon dots.
Types of photochromism 1 Positive photochromism
Negative photochromism
Mechanism of Phtochromism
Classification of photochromic materials
The lifetime of photochromic molecules should be longer (approx. 2 years) in both colored and colorless form.
Types of photochromic materials (T types) 1 Spiropyrans
Spirooxazines
The presence of different alkyl groups R at nitrogen atom determines the fading and color strength of molecules [32].
Napthopyrans/benzochromenes
P type photochromic materials
Fulgides
Diarylethenes
Effect of temperature
Applications in textiles 1 By exhaust dyeing
- By continuous dyeing
- Application of thermochromic materials
- Color measurement
- Washing fastness test
- Light fastness/photostability
Due to the reversible color change property of photochromic dyes, it is very difficult to measure the color value of the tint produced due to the photochromic effect. Due to the dynamic color changing properties of photochromic dyes, it is difficult to measure fastness properties. It was found that in selected spirooxazine dyes the degree of photo-staining increases with initial washing and then decreases.
With naptops, the degree of coloration of the photo steadily decreases with the successive number of washes. The normalized value is defined as the degree of coloration of the photo after a certain exposure time on the xenotest.
Thermochromism
The conventional method of exposing the sample to accelerated fading instruments (Xenotest or MBTF) does not apply to photochromic dyes. In photochromic dyes due to dynamic color change properties, a normalized value of color value must be calculated for lightfastness measurement.
Organic compounds
Liquid crystals
The pitch of the helical arrangement of the molecules determines the wavelength of reflected light [50].
Stereoisomerism
Inorganic thermochromic system
Microencapsulation
Application of thermochromic pigments on textiles 1 By exhaust method
Continuous method (In solution)
Application technique
Thermochromic cellulose fiber
Photochromic polymers
Textile printing
Sol –gel coating methods
Mass coloration
Conclusion
24]Christie R.M., Advances in Dyes and Dyestuffs, In Advances in the Dyeing and Finishing of Technical Textiles, M.L.
