Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Multi metal deposition <s> Operational details and optimisation of the colloidal gold or multimetal deposition technique (MMD) for the detection of latent fingermarks on non porous and porous surfaces demonstrate the power of the method. Control of particulate size, pH, reagent, handling are shown to be essential. A difficult case example illustrates the potential of MMD. <s> BIB001 </s> Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Multi metal deposition <s> Scanning electrochemical microscopy (SECM) has been used to image latent fingermarks enhanced by adsorption of gold nanoparticles onto which silver is chemically deposited, a process known as "multi-metal-deposition" (MMD). <s> BIB002 </s> Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Multi metal deposition <s> Among the numerous methods dedicated to the detection of latent fingermarks, the MultiMetal Deposition (MMD) offers, as a main advantage, the ability to be applied on a great number of porous and non-porous surfaces, e.g., paper, plastic, glass, latex, and polystyrene, even if wetted. While considered as a powerful and sensitive technique, MMD is often neglected, mainly because of operational limitations (siliconized vessels, restrictive pH domain, numerous immersion baths, ...). In this contribution, we propose a modification of the standard MMD method so that the procedure is simplified with a number of baths reduced to a minimum. To reach this goal, it was necessary to obtain a fully operable solution which could detect fingermarks in a single step. We chose to take advantage of the molecular recognition mechanisms by functionalizing the gold nanoparticles with a molecular host able to bind itself to gold while keeping the ability to trap molecules in solution. Cyclodextrins were chosen as they can be easily chemically modified to offer gold-binding abilities. Moreover, they are widely used as hosts for various molecular guests (dyes, luminescent molecules, ...). This new formulation has been tested on three different surfaces to attest the feasibility of this strategy. Successful results were obtained with detailed fingermarks offering a good contrast to allow their identification without the need to enhance the results (such as with a physical developer). If the new formulation behaves very similarly to the old one, in terms of experimental conditions, it offers the additional advantage to develop fingermarks after immersing them in only one bath. The goal is thus reached. <s> BIB003 </s> Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Multi metal deposition <s> The in situ deposition of zinc oxide on gold nanoparticles in aqueous solution has been here successfully applied in the field of fingermark detection on various non-porous surfaces. In this article, we present the improvement of the multimetal deposition, an existing technique limited up to now to non-luminescent results, by obtaining luminescent fingermarks with very good contrast and details. This is seen as a major improvement in the field in terms of selectivity and sensitivity of detection, especially on black surfaces. <s> BIB004 </s> Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Multi metal deposition <s> In this study we describe the use of gold nanoparticles as a fast detection system for the sensitive analysis of proteins. The immunological method allows for protein analysis at the nanogram level, as required for clinical diagnosis. Initially a test protein is used for the development of the assay. The system is subsequently adopted for alpha-fetoprotein, which is a relevant tumor marker. This work demonstrates that antibody functionalized gold nanoparticles can be used for the detection of proteins by forming gold nanoparticle aggregates. The influence of the size of the gold nanoparticles on the sensitivity of the assay is investigated in the range from 20-60 nm particles; the larger particles show here the highest relative changes. The formation of antigen-gold nanoparticle aggregates is detected by an increase in hydrodynamic diameter by dynamic light scattering (DLS). UV/Vis spectroscopy also allows assay monitoring by quantifying the red shift of the plasmon resonance wavelength. Alpha-fetoprotein can be analysed in the concentration range of 0.1-0.4 μg ml(-1). The influence of pH, ionic strength and ratio of sample to Au-NP solution is studied. With this method, the protein AFP can be rapidly detected as demanded for clinical diagnosis. <s> BIB005 </s> Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Multi metal deposition <s> This work is part of a continuing goal to improve the multimetal deposition technique (MMD), as well as the single-metal deposition (SMD), to make them more robust, more user-friendly, and less labour-intensive. Indeed, two major limitations of the MMD/SMD were identified: (1) the synthesis of colloidal gold, which is quite labour-intensive, and (2) the sharp decrease in efficiency observed when the pH of the working solution is increased above pH 3. About the synthesis protocol, it has been simplified so that there is no more need to monitor the temperature during the synthesis. The efficiency has also been improved by adding aspartic acid, conjointly with sodium citrate, during the synthesis of colloidal gold. This extends the range of pH for which it is possible to detect fingermarks in the frame of the MMD/SMD. The operational range is now extended from 2 to 6.7, compared to 2-3 for the previous formulations. The increased robustness of the working solution may improve the ability of the technique to process substrates that tend to increase the pH of the solution after their immersion. <s> BIB006 </s> Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Multi metal deposition <s> This paper reports a new and facile method for the synthesis of water-soluble thiolate-protected AuNCs via protein-ligand interaction. Using 3-mercaptopropionic acid (MPA) as a model ligand and bovine serum albumin (BSA) as a model protein, water-soluble AuNCs (BSA/MPA-AuNCs) with intense orange-yellow fluorescent emission (quantum yield=16%) are obtained. Results show that AuNCs produced with this method have hydrophobic interactions with BSA. The synthetic strategy is then successfully extended to produce water-soluble AuNCs protected by other thiolates. Moreover, a sensitive and eco-friendly sensing system is established for detection of the activity of inorganic pyrophosphatase (PPase), which relies on the selective coordination of Fe(3+)with BSA/MPA-AuNCs, the higher affinity between pyrophosphate (PPi) and Fe(3+), and the hydrolysis of PPi by PPase. A good linearity between the fluorescence intensity and PPase activity within the range from 0.1 to 3U/L is found, with a detection limit down to 0.07U/L. Additionally, the fluorescent assay developed here is utilized to assay the PPase activity in real biological samples and as well as to evaluate PPase inhibitor, illustrating the great potential for biological analysis. <s> BIB007 </s> Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Multi metal deposition <s> Abstract In this paper, we use an ion-exchange membrane disk to develop miniaturized concentration device, which employs gold nanoparticle (GNP) colorimetric assay to determine human serum albumin content in artificial urine samples. When an external field is applied across cation exchange substrate, the ion depletion appears on the anodic side when the ions are enriched on the cathodic side to fulfill mass conservation and electrical neutrality constrains. In particular when the ion exchange substrates are of round shape, the field lines passing through the membrane disk are focused at the exit pole to further enhance concentration polarization to result in a superconcentraiton spot. GNP colorimetric assays to determine albumin are carried out using the miniaturized concentration chip containing a Nafion ® cation-exchange membrane disk. Under alkaline condition when GNP solution is spiked with albumins to concentrate using the membrane disk, anionic albumins can prevent the concentrated GNP’s from aggregation and the concentrated GNP’s remain in red color even in highly salty solutions. On the other hand without efficient protections by absorbed albumins, GNP’s aggregate and change color to blue. Using smart phone camera to acquire the concentration images of non-aggregated nanoparticles, one linear correlation is found between the red color intensity and the logarithm values of albumin concentration to quantify albumin amounts. This colorimetric assay is validated to determine the samples of the main urine protein, human serum albumin at the range of clinical significance (0.1–20 μM) in artificial urine matrix containing creatinine and urine. These results prove the feasibility of using the membrane-based micro-concentration device with mobile phone camera. <s> BIB008
The idea of using colloidal gold nanoparticles in visualizing latent fingerprints on porous, non-porous, dry, and wet surfaces was first presented by Saunders in 1989 in a process known as multi-metal deposition (MMD or recently referred as MMD-I)  . The two-step process involves the initial deposition of metallic colloidal gold nanoparticles (~30 nm) onto the fingerprint residues (specifically amino acids), which subsequently act as nucleating sites for the secondary selective metallic silver deposition    . It has been reported that gold particles have been widely used in protein detection analyses BIB005 BIB007 BIB008 ). The addition of silver-based (modified PD) solution is considered advantageous since the poor contrast of colloidal gold nanoparticles-treated fingerprints (faint pink) would turn visibly dark BIB004   . Despite its universal ability in visualizing latent fingerprints on a wide range of porosity  BIB002 ), this silver-on-gold method is rarely applied in practical caseworks BIB006 , attributable to major drawbacks which include the use of expensive reagents and scrupulously clean glassware, laborious procedures (at least 1 h of processing due to the requirement of many immersion baths)   , and the possibility of over-development of prints BIB006  . In addition, MMD-I also suffers from limited working pH (~pH 3)  BIB006 ; at higher pH, significant decrease in the efficiency of the method was observed  BIB006 ). Such outcome is observed due to the loss of electrostatic attraction between the positively charged constituents of fingerprints (water-insoluble proteins that are trapped within the lipids) and negatively charged citrate-capped colloidal gold nanoparticles BIB001 BIB003  .  also mentioned that the post-treatment of visualized fingerprints with zinc (from zinc chloride) seemed to preclude the efficiency of MMD, since the formation of zinc ions subsequently interferes with the formation and stability of the colloidal gold solution  . Improvement in the operational performance of MMD-I was documented by BIB001 when the authors proposed an optimized modification to the conventional MMD-I, known as MMD-II. Apparently, the synthesis of smaller diameter of colloidal gold nanoparticles (~14 nm) followed by the use of hydroquinone/silver acetate developer in MMD-II proved to perform significantly better than MMD-I, with less reported background interference BIB001 . Despite such improvements, MMD-II still suffered from limited working pH range (pH 2.5-2.8), the need of numerous immersion baths, as well as extremely clean siliconized glassware. Since the numerous immersion baths are laborious and time consuming, BIB003 suggested a modification to the MMD-II method. The authors reported that thiolated cyclodextrins functionalized bare gold nanoparticles with the addition of Acid Blue 25 dye produced readily observable dark-blue prints in a single immersion bath. Although the modified method has been reported to have similar efficiency to the MMD-II in visualizing latent fingerprints (dry, wet, fresh, and aged) on various surface porosity, such method only works best at a restricted pH of 2.65 ).