Clinical Chemistry for Developing Countries: Mass Spectrometry

Abstract

Early disease diagnosis is necessary to enable timely interventions. Implementation of this vital task in the developing world is challenging owing to limited resources. Diagnostic approaches developed for resource-limited settings have often involved colorimetric tests (based on immunoassays) due to their low cost. Unfortunately, the performance/sensitivity of such simplistic tests are often limited and significantly hinder opportunities for early disease detection. A new criterion for selecting diagnostic tests in low- and middle-income countries is proposed here that is based on performance-to-cost ratio. For example, modern mass spectrometry (MS) now involves analysis of the native sample in the open laboratory environment, enabling applications in many fields, including clinical research, forensic science, environmental analysis, and agriculture. In this critical review, we summarize recent developments in chemistry that enable MS to be applied effectively in developing countries. In particular, we argue that closed automated analytical systems may not offer the analytical flexibility needed in resource-limited settings. Alternative strategies proposed here have potential to be widely accepted in low- and middle-income countries through the utilization of the open-source ambient MS platform that enables microsampling techniques such as dried blood spot to be coupled with miniature mass spectrometers in a centralized analytical platform. Consequently, costs associated with sample handling and maintenance can be reduced by >50% of the total ownership cost, permitting analytical measurements to be operated at high performance-to-cost ratios in the developing world.

Keywords: centralized detection; disease diagnosis; microfluidic paper-based devices; microsampling; open analytical systems; point-of-care; portable analytical systems.

Figure 1.

Representation of centralized system in African community; city, town, and villages.

Figure 2.

Distribution of mass spectrometers in developing countries is compared with other parts of the world. Number of mass spectrometers are counted from selected institution’s websites. Institutions are selected based on listed top 100 universities of the country at UniRank (http://4icu.org/). (A) Distributions of mass spectrometers in developing countries are shown in world map. For comparison of disparity of owned mass spectrometers, region of Ohio, United States and South Africa are selected. Approximately 43 instruments are found in five different institutions (University of Cincinnati, University of Akron, Ohio University, Cleveland State University, and The Ohio State University) in Ohio, USA. In South Africa, 67 instruments are owned by 18 different institutions (http://eqdb.nrf.ac.za/). Based on the collected database, ratio of number of instruments per institution are calculated for the following regions: (B) Ohio, (C) South Africa, and (D) South Asia.

Figure 3.

Comparison on different types of healthcare systems. The early model is provider-centered care, which can be transitioned to people-centered care. Major factors of shifting between two system include the fact that healthcare decision is made upon patients’ value and rights more than provider (e.g., doctor). This shift makes partnerships to manage not only individual health, but also in their community range. POC is still people-centered care, however real-time diagnosis or analysis at bed is a key.

Figure 4.

Schematics showing three major types of ambient ionization techniques: (A) spray-based, (B) plasma-based, and (C) substrate-based. Examples of spray-based ambient techniques include (Ai) Desorption electrospray ionization (DESI), (Aii) nano-desorption electrospray ionization (nano-DESI), and (Aiii) liquid microjunction surface sampling probe (LMJ-SSP) are described. Example of plasma-based techniques include (Bi) direct analysis in real time (DART), (Bii) transmission mode-direct analysis in real time (TM-DART), (Biii) Low Temperature Plasma (LTP), and (Biv) dielectric barrier discharge ionization (DBDI). Example of substrate-based methods include (Ci) paper spray (PS), (Cii) thread spray, and (Ciii) swab spray.

Figure 5.

Dry-state microsampling techniques are described for the (A) traditional absorptive-based and (B) a new adsorptive-based method. (Ai) Dried blood spots at different levels of blood hematocrit (above: 0.35 and bottom: 0.50 of blood hematocrit levels respectively). Figure adopted from Reference (CC BY-NC). (Aii) Volumetric absorptive microsampling (VAMS) device which enables the collection of accurate volumes (10 µL) of blood by absorption via a hydrophilic polymeric tip. Adopted with permission from Reference . (Aiii) Plasma extraction card is developed for rapid extracting plasma out of finger-stick blood. Alternative paper-based micro-sampling technology is developed based on adsorption phenomenon that occurs because of differences between surface tension of biofluids and surface energies of treated paper substrates. Adopted with permission from Reference . Hydrophobic paper substrates are prepared via a gas-phase silanization process (Bi), allowing three-dimensional (3D) spheroids of dried biofluids to be formed when a drop of biofluid is deposited and fully dried (Bii). Transient thermal analysis was simulated for a comparison between the 2D dried blood spots and the 3D blood spheroids (Biii). Panel (Bi) adapted with permission from Reference and panel (Bii and Biii) adopted with permission from Reference .

Figure 6.

Applications of microfluidic devices in mass spectrometry. (A) Microfluidic paper analytical device (PAD)-MS, which is developed by combination of immunoassay techniques and utilization of ionic probes (i), followed by subsequent MS analysis via touch paper spray ionization method once solvent is added (ii and iii). Adopted with permission from Reference . (B) Illustration of integrated multichannel microfluidic chip-MS which consist of a homemade manipulator, a hybrid capillary, a PDMS-glass microfluidic chip. Once cartridge droplet is generated, subsequent MS analysis is achieved via paper spray ionization with the aid of spraying solvent. Adopted with permission from Reference .

Figure 7.

Timeline in development of Mini-MS. In the 1990s, microelectromechanical systems (MEMS) were used in miniaturized mass spectrometers for the fabrication of compartments (e.g., analyzers and vacuum pump). Advancements have been made expanding development of miniaturized analyzers to include quadrupole mass filter, sector, time-of-flight (TOF), and ion trap. Figure reproduced with permission from Reference . Ion trap is currently the most common analyze due to qualities like high-pressure tolerance, ease of miniaturizing, and MS/MS capability. Therefore, the evolution of ion trap mass analyzers is described, which changed geometry from 3D hyperbolic quadrupole to 2D toroidal, 3D cylindrical, to 2D rectilinear, and finally to 2D halo ion trap. Figures reproduced with permission from Reference , and . The Mini-series (Purdue University, West Lafayette) are well-known examples of the ion-trap mini-MS system. Figure reproduced with permission from Reference . Besides ion trap evolution, continuous developments are being observed for other analyzers. These include chip-based quadrupole coupled to HPLC (Microsaic 3500 MiD, Microsaic Systems) and recently triple quadrupole mini-MS is invented which enables MS/MS. Figure reproduced with permission from Reference and Reference .

Figure 8.

Current applications of Mini-MS. (A) 50 ng of amitriptyline in blood is deposited onto the paper to form dried blood spot and analyzed with paper spray ionization on Mini 12. Adopted with permission from Reference . (B) The presence of fentanyls on the paper is identified via dual methods, portable surface enhanced Raman spectroscopy (Mira DS portable Raman spectrometer) and Mini-MS (Mini 12). Adopted with permission from Reference . (C) Targeted quantification of trypsin-digested methionine peptide from SKBR3 cell lysate is studied with Mini 12. Before MS analysis, immunoaffinity enrichment workflow is completed, and ionization is done with nano-electrospray technique. Adopted with permission from Reference . (D) Illustration of experimental setup for coupling microchip to mini-MS. Adopted with permission from Reference.